> Could you give me a link please? The Godot editor itself can't do multi-window and I haven't found a clear explanation on how to do that in the games either.

I think the functionality for multiple windows was added before this release but here's the 4.1 notes that you can open the code editor/other stuff in other windows: https://godotengine.org/article/godot-4-1-is-here/#editor

I just tried it and it seems to work.