Awesome, thanks for getting back to me and the helpful snippets. They put me on the path to solving the issue, and finally actually exploring kwin's window rules which I've been procrastinating on diving into.

I have one remaining issue though, and it appears to be with mpv, but maybe you have dealt with it before. No matter how much focus stealing protection I place on the mpv window in kwin, nor using the `--focus-on=never` argument with mpv, stops mpv from stealing focus when it launches. Any ideas? Otherwise I might try your idea about piping a playlist to mpv.

I don't use Wayland yet personally but I imagine that the mpv ontop mechanism might be conflicting with the focus stealing prevention. Do you use ontop? Does it work if you disable ontop? If so, this should probably be considered a bug in mpv on Wayland.

hmm maybe not: https://github.com/mpv-player/mpv/issues/9064

edit: I just verified it is working fine on X11 (wanted to make sure I wasn't mis-remembering--but it is very obvious when something steals focus because I use the Dim Inactive desktop effect with a very high setting). I'm using ontop=yes as mentioned before. On Fedora 39 with my setup mpv does not steal focus when launching/switching videos. I did notice some weird behavior with nomachine before but after setting Focus Protection to Force High for nxplayer.bin I haven't noticed it again.

    KWin version: 5.27.11

If this isn't working in Wayland surely this should be considered a Wayland/mpv bug?--just one more reason for me to delay trying Wayland

Awesome, thanks. Can confirm I'm not using `--ontop`, so at a bit of a loss. The issue is probably with mpv or Wayland because I get the same problem just launching mpv directly, without library. Although focus stealing protection in kwin seems to use some rubric around whether it thinks the window was spawned directly by the user or not to determine how the levels of protection are applied. I would have thought the highest level (extreme) would just prevent focus stealing entirely based on its description.

I'll see what I can do to debug the issue, but otherwise, thanks for your help, I might try your playlist idea in the meantime, it's arguably closer to my desired behaviour anyway.