Works basically flawlessly using Proton-GE-rtsp and OpenComposite. Haven't tried XRizer much, but from my usage it's seemed flawless for me. Documentation for setup on NixOS is pretty good, too. Nixpkgs overlays such as nixpkgs-xr for nightly builds of XR packages like Monado, Wlx-Overlay-s, Wayvr-Dashboard and others exist and makes it feel truly cutting edge. Performance is excellent with AMD only hardware 7900XTX and 5800x3D. Video players cause performance dips, but that's to be expected. Assuming 60fps, it will probably dip by about 10fps when looking at it or when it's active. FBT works flawlessly as long as STEAMVR_LH_ENABLE is set in the Monado environment.
Overall very nice experience.