I've had the same experience. I downloaded TT 2020 in Oct. December I "upgraded" the OS to Big Sur. Started taxes in Jan - all good. Then, a ~ week ago, it wouldn't open. Tried installing from the CD (purchased from Intuit). Loaded but wouldn't open. Spent an hour++ with nice but not very competent customer support. They even sent me another download, which I installed with the same result. What saved my bacon was emailing the data file, thankfully saved and not lost, to my wife's PowerBook with old (Catalina) OS. It loaded and worked (with some quirks) well enough to finish up. I think it had something to do with a Big Sur patch auto-installed in February that isn't compatible with TT 2020. Very poor coordination on the part of these two major players.
