AMD today announced that FidelityFX Super Resolution 3 (FSR 3) is now available in two games: Forspoken and Immortals of Aveum but the source code isn't up yet.
In regards to the source code being on GitHub like they've done with previous versions they simply said it "will be made available soon on GPUOpen with a permissive open source MIT license" so it could be later today, tomorrow or next month.
More games are planning to have FSR 3 added in like Eve Online, Frostpunk 2, Space Marine 2, Cyberpunk 2077, Squad, Crimson Desert, Avatar Frontiers of Pandora and more.
It's not clear currently how exactly FSR3 will work on Linux with Proton (or any future Native Linux games that get it). It's likely Proton will need some upgrades to support it properly. Testing the demo of Forspoken, which was also updated, just results in massive flickering issues making it quite unplayable and I really wouldn't recommend anyone try it as it will probably cause some seizures. As for Immortals of Aveum it seems FSR3 makes it crash.
At least once it gets fixed up properly on Linux, we might see some nice performance boosts from it.
See the AMD blog post for more.