Sorry you're having these problems and I guess I'd better knock on wood before I jinx my own working Turbotax HB. Have you see this thread?
https://ttlc.intuit.com/community/taxes/discussion/mac-os-big-sur-when-will-turbotax-run-under-this-...
Read through the whole thing then try the complete uninstall instructions and download the current TT version again. Maybe it will make a difference and solve the problem.
Also, if you still have TT2020 on your Mac, open that and let it update. I think I read someplace that updating TT2020 had a positive effect on the installation and operation of TT2021.
