For all those having the most recent Windows 11 update installed and having an Nvidia GPU: apparently the latest Windows 11 update indeed causes performance degratations, specifically with the Nvidia drivers:
Recent German IT article about this issue:
Apparently the issue is known to Nvidia and already fixed in their latest beta drivers, or so I understand.
Note that neither having Windows 11 nor an Nvidia GPU I can’t confirm this myself, but maybe that helps some.
UPDATE: Also see this existing discussion: