If you purchased your Mac with OS Catalina (10.15.x) or Big Sur (11.xx.x) already installed, you can skip the uninstall part above and follow the instructions below.

6 'high level' steps needed, follow down the page to make this a painless systematic process

1.Is your CAC reader 'Mac friendly'?
2.Can your Mac 'see' the reader?
3.Verify which version of Mac OS you have
4.Figure out which CAC (ID card) you have
5.Install the DoD certificates
5a.Additional DoD certificate installation instructions for Firefox users
6.Decide which CAC enabler you want to use (except for 10.12-.15 & 11)
Step 1: Is your CAC reader Mac friendly?
Visit the USB Readers page to verify the CAC reader you have is Mac friendly.
Visit the USB-C Readers page to verify the CAC reader you have is Mac friendly.
'Some, not all' CAC readers may need to have a driver installed to make it work.
Install
NOTE: Readers such as: SCR-331 & SCR-3500A may need a firmware update (NO OTHER Readers need firmware updates).
Information about these specific readers are in Step 2
Step 2: Can your Mac 'see' the reader?

Plug the CAC reader into an open USB port before proceeding, give it a few moments to install

Step 2a: Click the Apple Icon in the upper left corner of the desktop, select 'About This Mac'
Step 2b: Click 'System Report..' (button)
Step 2c: Verify the CAC reader shows in Hardware, USB, under USB Device Tree. Different readers will show differently, most readers have no problem in this step. See Step 2c1 for specific reader issues.
Step 2c1: Verify firmware version on your SCR-331, SCR-3310 v2.0, GSR-202, 202V, 203, or SCR-3500a reader. If you have a reader other than these 6, Proceed directly to step 3
Step 2c1a-SCR-331 reader
If your reader does not look like this, go to the next step.
In the 'Hardware' drop down, click 'USB.' On the right side of the screen under 'USB Device Tree' the window will display all hardware plugged into the USB ports on your Mac. Look for “SCRx31 USB Smart Card Reader.” If the Smart Card reader is present, look at 'Version' in the lower right corner of this box: If you have a number below 5.25, you need to update your firmware to 5.25. If you are already at 5.25, your reader is installed on your system, and no further hardware changes are required. You can now Quit System Profiler and continue to Step 3.
Step 2c1b-SCR-3310 v2.0 reader
If your reader does not look like this, go to the next step.
In the 'Hardware' drop down, click 'USB.' On the right side of the screen under 'USB Device Tree' the window will display all hardware plugged into the USB ports on your Mac. Look for “SCR3310 v2.0 USB Smart Card Reader.” If the Smart Card reader is present, look at 'Version' in the lower right corner of this box: If you have a number below 6.02, it will not read the 'G+D FIPS 201 SCE 7.0' CAC on Mac OS 11.xx.x or 10.15.7. I contacted HID (the company that makes these readers) on 14 DEC 2020 to find a way to update the firmware to 6.02. They said there is not firmware update for the reader. If your reader is older, you may need a new one. Please look at: https://militarycac.com/usbreaders.htm to find a compatible one. If you are already at version 6.02, your reader should work fine on your Mac and no further hardware changes are required. You can now Quit System Profiler and continue to Step 3.
Step 2c1c-SCR-3500A reader
If you have the SCR3500A P/N:905430-1 CAC reader,you may need to install this driver, as the one that installs automatically will not work on most Macs. Hold the control key [on your keyboard] when clicking the .pkg file [with your mouse], select [the word] Open
Step 3: Verify which version of MacOS you have?
(You need to know this information for step 6)
Step 3a: Click the Apple Icon in the upper left corner of your desktop and select 'About This Mac'
Step 3b: Look below Mac OS X for: Example: Version 10.X.X, or 11.X
Step 4: Figure out which CAC (ID Card) you have
(You need to know this information for step 6)
Look at the top back of your ID card for these card types. If you have any version other than the six shown below, you need to visit an ID card office and have it replaced. All CACs [other than these six] were supposed to be replaced prior to 1 October 2012.
Find out how to flip card over video
Step 5: Install the DoD certificates (for Safari and Chrome Users)
Go to Keychain Access

Click: Go (top of screen), Utilities, double click Keychain Access.app

(You can also type: keychain access using Spotlight (this is my preferred method))

Select login (under Keychains),and All Items (under Category).

Download the 5 files via links below (you may need to <ctrl> click, select Download Linked File As.. on each link) Save to your downloads folder
Please know.. IF You have any DoD certificates already located in your keychain access, you will need to delete them prior to running the AllCerts.p7b file below.
https://militarycac.com/maccerts/AllCerts.p7b,
https://militarycac.com/maccerts/RootCert2.cer,
https://militarycac.com/maccerts/RootCert3.cer,
https://militarycac.com/maccerts/RootCert4.cer, and
Double click each of the files to install certificates into the login section of keychain
Select the Kind column, verify the arrow is pointing up, scroll down to certificate, look for all of the following certificates:
DOD EMAIL CA-33 through DOD EMAIL CA-34,
DOD EMAIL CA-39 through DOD EMAIL CA-44,
DOD EMAIL CA-49 through DOD EMAIL CA-52,
DOD EMAIL CA-59,
DOD ID CA-33 through DOD ID CA-34,
DOD ID CA-39 through DOD ID CA-44,
DOD ID CA-49 through DOD ID CA-52,
DOD ID CA-59
DOD ID SW CA-35 through DOD ID SW CA-38,
DOD ID SW CA-45 through DOD ID SW CA-48,
DoD Root CA 2 through DoD Root CA 5,
DOD SW CA-53 through DOD SW CA-58, and
DOD SW CA-60 through DOD SW CA-61
NOTE: If you are missing any of the above certificates, you have 2 choices,
1. Delete all of them, and re-run the 5 files above, or
2. Download the allcerts.zip file and install each of the certificates you are missing individually.
Errors:
Error 100001 Solution
Error 100013 Solution
You may notice some of the certificates will have a red circle with a white X . This means your computer does not trust those certificates
You need to manually trust the DoD Root CA 2, 3, 4, & 5 certificates
Double click each of the DoD Root CA certificates, select the triangle next to Trust, in the When using this certificate: select Always Trust, repeat until all 4 do not have the red circle with a white X.
You may be prompted to enter computer password when you close the window
Once you select Always Trust, your icon will have a light blue circle with a white + on it.
The 'bad certs' that have caused problems for Windows users may show up in the keychain access section on some Macs. These need to be deleted / moved to trash.

How To Install Yosemite

The DoD Root CA 2 & 3 you are removing has a light blue frame, leave the yellow frame version. The icons may or may not have a red circle with the white x
or DoD Interoperability Root CA 1 or CA 2 certificate
DoD Root CA 2 or 3 (light blue frame ONLY) certificate
or Federal Bridge CA 2016 or 2013 certificate
or Federal Common Policy CAcertificate
or or SHA-1 Federal Root CA G2 certificate
or US DoD CCEB Interoperability Root CA 1 certificate
If you have tried accessing CAC enabled sites prior to following these instructions, please go through this page before proceeding
Clearing the keychain (opens a new page)
Please come back to this page to continue installation instructions.
Step 5a: DoD certificate installation instructions for Firefox users
NOTE: Firefox will not work on Catalina (10.15.x), or last 4 versions of Mac OS if using the native Apple smartcard ability
Download AllCerts.zip, [remember where you save it].
double click the allcerts.zip file (it'll automatically extract into a new folder)
Option 1 to install the certificates (semi automated):
From inside the AllCerts extracted folder, select all of the certificates
<control> click (or Right click) the selected certificates, select Open With, Other..
In the Enable (selection box), change to All Applications
Select Firefox, then Open
You will see several dozen browser tabs open up, let it open as many as it wants.
You will eventually start seeing either of the 2 messages shown next
If the certificate is not already in Firefox, a window will pop up stating 'You have been asked to trust a new Certificate Authority (CA).'
Check all three boxes to allow the certificate to: identify websites, identify email users, and identify software developers
or
'Alert This certificate is already installed as a certificate authority.' Click OK
Once you've added all of the certificates..
• Click Firefox (word) (upper left of your screen)
• Preferences
• Advanced (tab)
• Press Network under the Advanced Tab
• In the Cached Web Content section, click Clear Now (button).
• Quit Firefox and restart it
Option 2 to install the certificates (very tedious manual):
Click Firefox (word) (upper left of your screen)
Preferences
Advanced (tab on left side of screen)

Can I Install Yosemite On My Macbook Computer

Certificates (tab)
View Certificates (button)
Authorities (tab)
Import (button)
Browse to the DoD certificates (AllCerts) extracted folder you downloaded and extracted above.
Note: You have to do this step for every single certificate
Note2: If the certificate is already in Firefox, a window will pop up stating: 'Alert This certificate is already installed as a certificate authority (CA).' Click OK
Note3: If the certificate is not already in Firefox, a window will pop up stating 'You have been asked to trust a new Certificate Authority (CA).'
Check all three boxes to allow the certificate to: identify websites, identify email users, and identify software developers
Once you've added all of the certificates..
• Click Firefox (word) (upper left of your screen)
• Preferences
• Advanced (tab)
• Press Network under the Advanced Tab
• In the Cached Web Content section, click Clear Now (button).
• Quit Firefox and restart it
Step 6: Decide which CAC enabler you can / want to use
Only for Mac El Capitan (10.11.x or older) 1tb chip for macbook air.
After installing the CAC enabler, restart the computer and go to a CAC enabled website
NOTE: Mac OS Sierra (10.12.x), High Sierra (10.13.x), Mojave (10.14.x), Catalina (10.15.x), and Big Sur (11.1) computers no longer need a CAC Enabler.

Can I Install Yosemite On My Macbook Pro

Try to access the CAC enabled site you need to access now
Mac support provided by: Michael Danberry
I will be the first to admit that I prefer Windows over Mac OS any day. Besides being a slight Microsoft fanboy, I do prefer Windows because it meets all of my software and gaming needs, but I digress. In any case, there are still some unfortunate situations when I need to have access to Mac OS.
Luckily, I’ll show you an easy way on how to install Mac OS X Yosemite on any pc, regardless of the hardware that you currently have installed (even if it is an AMD CPU). Doing this will require a specially modified version of Yosemite called Yosemite-zone.dmg. With a quick Google search, you should be able to find it. As far as performance, I did not encounter any issues. It ran surprisingly smooth even before setting up Multi-beast. Of course, ymmv.

What You Will Need:

Step 1: Format GPT

The first thing that you need to do is restore the Yosemite-zone.dmg image to the USB. Open transmac, and right click on your USB. First, select the option to format for Mac (this will change the boot record from MBR to GPT). Once it completes, select the option to restore the disk image to the USB. It will take about 10 minutes to restore the image. Finally, right click the hard drive_ _that you want to install Mac OS to choose the option to format for Mac. Keep in mind that you will need a separate hard drive for the Mac OS installation. You will not be able to solely format one partition.

Step 2: Bios

Before you boot from your USB, go into your bios settings. This part can get a little complicated depending on your hardware. Make sure that you have secure boot disabled and Vt-D. Also, when you choose boot devices, make sure your USB is not booting with Eefi. Fortunately, I did not have to change anything and kept my bios to the default settings.

Can I Install Yosemite On My Macbook Pro

Step 3: Boot from USB

Now boot from the USB. You should see a boot loader screen that will prompt you with what operating system/hard drive to boot with. At the bottom of the screen, you can enter boot flags. If you are using an AMD CPU type in “/amd”, or “/amd32” or “/amd64”. If you run intro trouble during installation, check out these other boot flags that you can use. If you don’t need to type in anything, simply choose Yosemite from the selection window.

Step 4: Setup

From this point, you will be taken through the standard Mac OS setup. If you already set up your drive in Windows using TransMac, than you can just skip to the installation. If not, make sure to go into Disk Utility and format your desired hard drive. The installation should take about 16 minutes. Once it’s done it will reboot your PC. Remember to reboot from the hard drive Mac OS is installed on (if that fails, try rebooting from the USB again).

Can I Install Yosemite On My Macbook

Step 5: The Final Steps

Can I Install Yosemite On My Macbook Pro 2018

From this point, you can go through the normal setup process for Mac OS. As far as compatibility, all my existing hardware worked fine with Mac OS. This included speakers and internet. Of course, you can always install MultiBeast to add any post secondary drivers and optimizations.