I consider it unplayable at least, at my native 1440p res it frequently drops to ~20ish FPS (RTX 2080). On AMD the game runs fine under Linux with DXVK (Laptop and Steam Deck).
ive just tested the game for about an hour on Arch Linux, RTX 3080, i7 11700k, 32gb of ram, and can say that i didnt see any graphical glitches anymore, and the performance seems to be “perfect” again. quite similar to windows, if not better.
i already gave the people in the github tracker (Sonic Frontiers (1237320) · Issue #6303 · ValveSoftware/Proton · GitHub) a heads up that it seemingly now works. maybe some others will test it, too.
I tested it with 535.104.05 and also can no longer reproduce the severe performance issues. It runs pretty ok now.
Sometimes performance still drops to 30-40 fps at seemingly random times, so it’s not quite perfect. It recovers just as mysteriously after some time, despite just standing still. That could be a different problem though, maybe with the engine’s frame limiter misbehaving or something. And no, it’s not shader compilation stutter.