So, good news: Unreal Engine 5 Editor on Wayland is 90% of the way there:

https://twitter.com/flibitijibibo/status/1511530172553605124

Bad news: T̴̰͛h̴̨͑ë̴̗ ̵̥̇ö̴͖́t̴̫̽h̷̰̀e̸̢̔r̵̫͐ ̶͚̆9̴̟̇0̸̠̿%̶͍̌ ̵̙̑c̶̝̔o̶̭̓m̴͎̆è̶͕t̵̎ͅh̷̦͘

It's really down to two halves: One is on Epic's end (global window/mouse position dependency), the other is on ours: We need to add support for SDL_WINDOW_TOOLTIP and SDL_WINDOW_POPUP_MENU. This is in the xdg_shell spec as a surface role from what I remember, but despite this being assigned to me I have no idea what I'm doing here and literally never work on tools, so I wouldn't know the first thing about implementing this correctly. If you're a tools programmer, this is probably very straightforward!