Hi, I've spotted the same issue, and I needed to get back my files that were stuck somewhere in the system.
My steps to fix that issue - I've followed the steps with reset NVRAM, which didn't work for me 30% of the progress, and it stopped.
Please read step by step to save your files from being wiped out.
Turn off your Mac
Start with the pressed Shift button https://support.apple.com/pl-pl/guide/mac-help/mh21245/mac
Log in to Your profile and wait. There will be steps like on the new mac with all configuration steps. Don't be afraid your files are safe.
When You get a "new" profile. Go to the terminal and find your previous account. You can copy those files to that new profile. (please check that in the terminal guide)
https://support.apple.com/guide/terminal/manage-files-apddfb31307-3e90-432f-8aa7-7cbc05db27f7/mac
cp -R ~/Documents/Expenses /Volumes/Data/Expenses
To backup files, you need to use some cloud storage (in safe mode, you can't use an external drive). https://support.apple.com/guide/terminal/manage-files-apddfb31307-3e90-432f-8aa7-7cbc05db27f7/mac
When you copy files to cloud storage, You need to do a new clean installation of Big Sur https://support.apple.com/en-us/HT204904
I hope that will help someone