Same problem here.
AMD RX6600 8GB GPU
AMD Ryzen 5 5600X 6-Core Processor 3.70 GHz
RAM 20,0 GBs
Win10 64
All works fine until I’m trying to use upper menus (file, edit, etc…). At the moment before appearance of menu a freeze happens: stops all system: mouse movements, sound, etc for like 10 seconds.
If i have some application which can use ‘always on top’ mode (like mplayer or pureref) - lag do not occurs.
Updating GPU drivers and UE to 5.1.1 version didn’t fix the problem.