I’m not completely sure but what I did for neovim could be relevant / helpful? Iirc then you can’t control things like window icons or the position of the window itself because it’s controlled by the compositor in this case Wayland which ignores those hints. I used a .desktop workaround in my case which should work for you too.
My post:
I’m essentially targeting the window by its title with a KWin Script then setting its “Desktop file” option to neovim you could try the same with your yad window since the title arg is respected by Wayland
More info: