Plex Server running under Windows 11 about on 7/22/2021 stopped movie playback

Pull the log files and check the Plex Media Server.log file for error messages containing “database locked.”

Example:
ERROR - Failed to begin transaction (..\Plugins\PluginDatabaseState.cpp:110) (tries=10): Cannot begin transaction. database is locked

If you see the messages, then see the below thread for a hotfix build and status updates.