Hi boococp
I encounter a similar issue when connecting my Mac (Big Sur 11.2.3) to a NAS using SMB, but a workaround is available.
It works for me, I found it here: https://developer.apple.com/forums/thread/661437
Open terminal and type the following command:
sudo /usr/libexec/configureLocalKDC
It also works for the other connected users. However it is not persistent, so after a reboot you need to type it again.
It's referenced as a fix for a similar issue in a security update for macOS 10.13:
https://support.apple.com/en-us/HT208317
Maybe somebody has a suggestion to make the change persistent ?