If you delete a user account in some versions of macOS (Monterey in my case) where the user account was created in certain earlier versions of macOS you will run into a System Integrity bug.
There's a folder called VoiceTrigger that in the deleted user account that is protected by System Integrity (~/Library/VoiceTrigger/SAT. ) It's located in the User's Library, so it should not be SIP protected. (In Monterey there's nothing there called SAT).
I'm guessing the bug is that it was never supposed to be SIP protected but in some version of macOS it was. Maybe Big Sur. (There's a second bug because the error message is incorrect. The problem isn't that the file is in use, the problem is it's SIP protected.)
I found the fix in in r/MacOS - disable SIP, delete, re-enable SIP:
Things other's suggested that didn't work:
1. Terminal: sudo rm -rf ~/.Trash/*
Note you need to be admin to do this. There's a way to escalate non-admin to use sudo but I think Apple has basically given up on non-admin user accounts.
2. Turn off iCloud document sync.