This has worked on my macOS Big Sur. I upgraded by transferring my data to a new MacBook Pro. Then my interface stopped working for an unstated reason.
The problem with the RA T4 is that the installer checks for a known version of the OS and fails on Catalina and above. But we can extract the components of the installer and install them manually.
Download the https://macpaw.com/the-unarchiver . Install it.
Download the latest driver for T4 or T2 from ResidentAudio.com.
Unpackage the contents of the T4 driver by right clicking in the Finder and selecting, using Open With->The Unarchiver. Do this to all the contents the first layer does and so forth on the second layer, recursive.
When thats finished:
Open the Scripts folder and its two files 'preinstall' and 'post install' . I think best to not run the preinstall as it mainly deletes previous installation.
Use the 'content' of the uninstall script below to copy the contents to the correct folders:
That last two lines, I don't understand but it worked for me without it.
Open the Scripts folder and its two files 'preinstall' and 'post install' , open a terminal and prefix 'sudo' then drag the 'postinstall' in the Terminal to get the path and file to appear after your typed sudo. Press return and type the password.
My mac required a restart before it worked. It doesn't seem to work with hot swap without a restart. I have a StarTech TB3 to TB Adaptor and would be interested in whether a Apple TB3toTB adaptor works with hot swap or what is required to get hot swap going.
If you ended up buying a new audio interface, learn how to use Multiple Audio Interfaces - Aggregate Device in OSX