We’ve seen a number of reports like this, but have yet to nail down the cause.
The latest version of Big Sur is 11.7.10. Updating helps some people, but not all. This does seem to be exclusively a Big Sur issue, so if your hardware will support a newer version of Mac OS you might consider upgrading.
Reinstalling the latest version of Scrivener from a fresh download helps some people, but not all.
As @November_Sierra said, reverting to the previous version is a safe workaround. Your work is stored separately from the Scrivener application and should be fine. (Although making an extra backup is never a bad idea.) You can download the previous version here:
https://www.literatureandlatte.com/downloads/Scrivener_3.3.1.zip