I'm also having this problem.
When I originally updated to Big Sur, I was able to get R2021a to open by changing the Full Disk Access settings as Dmitry suggested.
Big Sur automatically updated again last night, and I'm now on version 11.2, and MATLAB won't open this morning. The logo pops up and stays open, but the IDE never presents itself. The disk privileges fix that worked last time doesn't work anymore. I can't even open R2021a from the command line with sudo privileges by typing:
Is there a permanent fix for this? I've honeslty found Big Sur extremely buggy. Have others had a similar experience with the updated OS?