Please refer these steps, see if they could help:
- Run regedit command to open Registry Editor.
- Go to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System.
- Under System, set HideFastUserSwitching registry DWORD (REG_DWORD) to 0 value data.
- Close Registry Editor and restart your system to make changes effective.
P.S. If you're new to registry, create a System Restore point before try above steps.
If issue still persists, refer other suggestions in this fix:
https://www.kapilarya.com/fix-cant-switch-users-in-windows-11
Let us know if this helps!
Note: Included link(s) in this reply refers to a non-Microsoft website. The page appears to be providing accurate, safe information. Watch out for ads on the site that may advertise products frequently classified as a PUP (Potentially Unwanted Products). Thoroughly research any product advertised on the site before you decide to download and install it.