HOW TO RESTART MY MAC WHEN IT WON’T RUN FINDER?
Because of differences from older versions, upgrading to Big Sur or Monterey can cause problems, and you may be asked to turn off FileVault first. When you do that, the volume isn’t necessarily decrypted immediately. The process can take a long time, so you should leave your Mac running and awake for a day or two before assuming that it won’t decrypt.