Again using parent's example of AwesomeWM: You'll temporary move one of the "windows" to the same "screen" as the other one (via "tagging"), resetting everything once you're done. Usually this is like 2 or 3 shortcuts all together.

AwesomeWM uses a tag system for windows, so you assign windows to one or more tags, then you can freely view one or many tags at the same time, compared to the traditional "workspaces" approach that for example Gnome and macOS has.