Variable rate refresh (VRR / FreeSync / Adaptive-Sync) support for GNOME’s Mutter compositor is closer to being merged. The native back-end support for VRR that has been in development the past two years is no longer considered a work-in-progress and it’s believed there are no longer any blocking issues that would prevent this code from landing.
Every modern compositor should support this.
Note that one of the things holding it back is that a standard protocol for communicating VRR support status under Wayland hasn’t been settled on yet and Mutter’s current MR just blindly assumes all clients (i.e. applications) won’t break or glitch if the user toggles VRR on.