Where can I get the Compatibility Matrix for Remedy 20.02?

You can check the BMC SOLUTION AND PRODUCT AVAILABILITY AND COMPATIBILITY UTILITY (SPAC) in the Support site.
Link: https://docs.bmc.com/docs/compatibility/

There it will be listed all the requirements for AR System.
To get the actual Compatibility Matrix, you need to search for the required product

Once you select the required version, you will get the detailed information as show in the following image:

Also, you can get compatibility matrix in PDF format. See BMC Remedy ITSM Suite compatibility matrix