Not sure why 12.0 is not supported, because the major change for macOS -- the 64 bit (cocoa) front end, is in 12.0. It is possible that Stephen missed it (or I did -- I'll check the video). Things may still be fluid, so a message to tech support may help.
I am running 12.2 beta on my Big Sur beta, and it's pretty impressive. Lots of new stuff and fixed up stuff.
Even if you want to wait, the 12.1.1 update had hundreds of bug fixes, some of which may be of interest to you.