Failed to acquire mutex for user - user can't logoff

I had the same issue, I resolved this by disable the three new features by GPO, enabled by default in this new version of FSLogix - disabling both disc compaction, roaming of recycle bin and appx-packages through GPO - then a restart of the VDAs or RDSH if you're not using Citrix.

You can try disabling one at a time, my money is on disc compaction or roaming of the recycle bin

"Changes
Feature: Added the ability to compact the user's container during the sign-out phase. For more information, see VHD Disk Compaction.

Feature: Added a new process during the sign-out phase which creates an AppX package manifest for the user. This manifest is used at sign-in to re-register the AppX applications for an improved user experience. This work is on-going as AppX packages and applications continue to evolve. The focus for this work has been on the built-in Windows apps (inbox apps).

Feature: We will now roam the users Recycle Bin within the user's container.

Important

All three (3) of our new features are enabled by default, but have the option to be disabled."

https://learn.microsoft.com/en-us/fslogix/whats-new#:~:text=Changes,to%20be%20disabled.