

Everything runs under Wayland. That should be your default expectation.
At this point, Wayland is the preferred environment for GTK and Qt apps. Unless the app is exploiting some specific aspect of X11, all GTK (3 and up) and Qt (5 and up) apps work fine under Wayland.
As for other toolkits, FLTK, Electron, and SDL apps run in Wayland too.
And by “preferred”, I mean that these apps (like Thunar) will run natively on Wayland even if Xwayland is available.
There are Wayland only toolkits now but not really any “modern” toolkits that do not support Wayland. When Thunar gets ported to GTK5, it will be Wayland only.
Obviously ancient x11 specific stuff like XCB or Athena, and things built on them like Motif will require Xwayland or Xsatellite. So if you want to run, xv or motif nedit, you need those. This list includes GTK2 as well. But even they work well enough you may not notice. I mean, xeyes won’t track your mouse I guess.
And just in case mentioning xeyes brings out the Wayland critics, you can build an xeyes app that works in Wayland. I think the Wayland Maker compositor project has one for example (WindowMaker in Wayland).
With all the bleating about how GNOME does not listen to users, these kinds of little quality of life improvements may be more significant than you think. Let’s hope we see more of them.