I just ran through this with an apple tech, still in progress but will append if it changes in 1 hour 38 minutes remaining Boot into Recovery mode in terminal enter resetpassword it will be confirmed with technical gibberish which means something to someone else. recovery assistant will come up behind the terminal window choose your disk and erase it, computer will restart when finished on restart, it came up in recovery again and I selected install macOS Big Sur The drive is labeled as "Untitled" now rather than Mac HD but I was told it should revert to Macintosh HD when done.