I just wrote a "program" (ok, tiny utility) that behaves like you describe, but don't worry, it's for my personal use so you you won't have to deal with it :)

(i run it when I have an image in the clipboard and it shows an always-on-top window with that image. i can drag it around but it doesn't take focus. it's so on my single monitor setup (aka laptop on the couch) I can take a snapshot of something and then easily reference it in a maximized/semi-fullscreen application). I honestly mostly wrote it to see how fiddly winapi stuff from rust is but I actually end up using it a bunch)

I see where Wayland is coming from but I've come around to preferring the chaos of every app getting to do whatever it wants over hoping that various compositors are willing to support some obscure special case some app or other might want. Like, it sucks if apps are misbehaving but it sucks more if you can't reasonably fix an app to behave like you want it at all.