I am not super familiar with Wayland, but basically how composited rendering under X11 works, is if you have a fullscreen window, you can give an 'unredirect' hint to the compositor, in which case when nothing else is drawing your screen, it will stop compositing, and pass your app's swapchain directly to the screen.

This is pretty much optimal, and you can't really do much better than this.

Once a stray window appears on top, or something makes the compositor think it can't do this, it'll do the intermediate step of compositing your app window with others into a temp buffer, and render that.

Sometimes the unredirect breaks for some reason (I remember a case where for some inexplicable reason my app kept creating a window 1px smaller than the screen height), or you use XWayland, you get bad latency.

Since this is a fundamental constraint, other compositors on different OSes must work like this, and you can run into issues like this as well.

Another thing - Wayland afaik started exporing 'display planes' - which are a HW feature of GPUs, that allow it to composite multiple layers together - which means the game can render at full FPS and all the windows on top will be drawn into a different plane and get composited with no ill effects - not sure if this is actually used in production yet.