Wayland intellij ide support is in the works, IDEs support X11 out of the box, but you can enable Wayland support explicitly (just search for it).
As per Windows placement, Firefox won't restore windows on original positions supposedly because of Wayland, somebody please correct me if I'm wrong.
Intellij kinda supports Wayland, but it gets confused when using scaling, at least when not all screens have the same factor. It's not blurry or anything, but it's slower, and the menus sometimes appear in random places.
When I only use a scaling factor of 1 on all the screens, it's usable enough, although it still feels sluggish.
You are not wrong. But there is a new extension protocol on the way (dunno if done, very probably not rolled out if it is) that let programs solve this problem.
Uh, there are plenty of extensions. Session management perhaps? In experimental state.
Uh, was thinking of one that explicitly deals with window positioning of new windows.