This MR just got merged: https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/19125
Which completes the tearing protocol: https://gitlab.freedesktop.org/wayland/wayland-protocols/-/merge_requests/65
So once the mesa update lands, XWayland titles should be able to tear under Wayland, at least on AMD GPUs. Nvidia will have to provide support in their drivers in the future.
I’m too lazy to turn Freesync off on my monitor, so I guess it’ll be working when I upgrade mesa.