I was having a terrible time with slowdowns on all versions of 4.x. I'm talking over 30 seconds from pressing run to my app starting. The console output would not update on app opening for another 20 seconds or so.
I seem to have fixed this by: - deleting .godot in my app folder. - deleting my appuserdata shader cache and - deleting the AppData\Local\Godot folder.
Posting this in case it helps anyone else. Was driving me nuts.
System: Godot Engine v4.1.1.stable.official.bd6af8e0e (and prev 4.x releases), OpenGL API 3.3.0 NVIDIA 472.47 - Compatibility - Using Device: NVIDIA - NVIDIA GeForce RTX 2070 SUPER Win 10. i7-6700, 32GB RAM.