Well, that only works for GTK 3 or 4 apps. Thanks to CSDs and GNOME's refusal to implement SSDs, every app that's not either running in XWayland or a GTK3/4 app has its own decorations without the context menu with the always on top option.
There was some way of enabling always on top on non-GTK3/4 apps too, but I don't remember it off the top of my head.
You can use the alt+space shortcut to access the window context menu on any window, even if they are not a gtk/gnome app. At least on my system qt and kde apps still get some kind of ssd decoration that behaves somewhat like the gnome apps, plus access to the window context menu, though I agree things should be better than this and work more universally...
There was some way of enabling always on top on non-GTK3/4 apps too, but I don't remember it off the top of my head.