What's sad is that after many years Wayland still lacks several things/features that X11 has/allows. Some of them are intentionally not implemented because of security paranoia. For example, Chrome "picture in picture" window doesn't stay on top when I click somewhere else since Wayland doesn't allow windows to stay on top. If I had a lot of time I could list how Wayland breaks many applications.
Not saying that X11 is not broken and should not be replaced, but many Wayland's decisions harm user experience more than X11.
I have a virtual pinball cab with two (and soon) three displays. Wayland really makes life difficult here because the software needs to always put the playfield on one display, the backglass on another, and the "dot matrix display" window on a third. That's a big no-no with Wayland. Fortunately KDE has window rules as a workaround. Sway and Hyprland allow similar rules. Mutter on Gnome has no equivalent.
I'm guessing this would mess up other games as well, like multi-screen flight simulators or driving games. It would be really nice if user-trusted apps could be granted permissions on an app-by-app basis to allow absolute placement of windows for these cases instead of making us jump through hoops.
Ah, for some reason I figured this was a minor bug that'd be fixed eventually. Wayland windows are never allowed to spawn always-on-top? Sort of lame.
If the logic is that it's the window manager's job to set window rules for this, fine, but in that case Plasma should probably ship with preconfigured rules matching the Chrome/Firefox PiP window.
I also find the lack of an Xlib-compatible macro API disruptive but I usually run an X11 session inside Xvnc for this purpose anyway.
I know nothing about the detailed technical differences between X11 and Wayland but with Hyprland for me the PIP is working as expected so I assume its not just a Wayland issue but specific to the window manager you are using? Maybe somebody else can explain?
I can't speak for Chrome, but I can right click a Firefox picture-in-picture window, tell it to remain on top, and it does, no problem. I've been using Plasma Wayland for years now and this has worked for ages
I fixed this like this:
1. Right click PIP window 2. More Actions -> Configure special window settings 3. Add property -> Layer Force Popup
After this it spawned always in middle, I also added property Position Remember, so it spawns where it was previously. I have no idea if this is the best way to fix but worked for me.
If you use KDE, you can work around this because of the powerful feature set the window manager has for setting custom window behavior.
1. Right click the PIP window and then click "More Actions-> Special Window Settings".
2. On the window that pops up, click "Add Property", and add "Window title". Change the drop-down from "Unimportant" to "Exact match" (this works on Firefox because the window title is always "Picture-in-Picture", you might have to do something slightly different on Chrome if it does something different).
3. Click "Add Property" again, add "Keep above other windows", change the drop-down to "Force", and change the radio button to "Yes".
4. From now on, all PIP windows will show up on top of other windows.
It would definitely be nicer if there was some sort of "always on top" permission that applications could request, but it's not too bad.