Now if there was just an official API from all window managers that can check this configuration
This actually does exist. Reasonable Wayland Compositors will negotiate with their clients on whether they should use CSDs or SSDs. To an extent Qt does this: It prefers SSDs but it can draw CSDs if the compositor can’t draw SSDs (or signals that it doesn’t want to), which is why proper Qt apps are perfectly usable on GNOME Wayland despite missing SSDs.
It would be possible to go even further and make apps that display menu and tool bars on compositors that prefer SSDs (like Plasma/KWin) and nice GTK-style decorations on others. It just happens that most apps either really want to draw their CSDs (mostly because they’re made for GNOME, a.k.a. anything using Libadwaita) or they don’t really have a use for them (like regular Qt apps).
This actually does exist. Reasonable Wayland Compositors will negotiate with their clients on whether they should use CSDs or SSDs. To an extent Qt does this: It prefers SSDs but it can draw CSDs if the compositor can’t draw SSDs (or signals that it doesn’t want to), which is why proper Qt apps are perfectly usable on GNOME Wayland despite missing SSDs.
It would be possible to go even further and make apps that display menu and tool bars on compositors that prefer SSDs (like Plasma/KWin) and nice GTK-style decorations on others. It just happens that most apps either really want to draw their CSDs (mostly because they’re made for GNOME, a.k.a. anything using Libadwaita) or they don’t really have a use for them (like regular Qt apps).
Nice, I didn’t know about that. But the problem with Wayland is like always it takes too long. That’s why nobody implements it.