OK in principle, but I'd feel safer if a few people (with different GPUs) tried this on their 20.09 system before we merge it into release-20.09. We had an unpleasant regression like this once.

It should be sufficient to test without a large rebuild. In past I've been using config like this (adapted to current version):

{
  imports = [
    (let mkDrivers = pkgs: (pkgs.mesa.overrideAttrs (a_: rec {
          branch = "20.1";
          version = "${branch}.10";
          src = pkgs.fetchurl {
            urls = [
              "ftp://ftp.freedesktop.org/pub/mesa/mesa-${version}.tar.xz"
              "ftp://ftp.freedesktop.org/pub/mesa/${version}/mesa-${version}.tar.xz"
              "ftp://ftp.freedesktop.org/pub/mesa/older-versions/${branch}.x/${version}/mesa-${version}.tar.xz"
              "https://mesa.freedesktop.org/archive/mesa-${version}.tar.xz"
            ];
            sha256 = "17zfqvc3q2pxy2bjwg8zp5sqqjlsv4rpizdx9k5rzb5d22csdnxi";
          };
        })).drivers;
      #pkgs = import (builtins.fetchTarball https://github.com/nixos/nixpkgs/archive/nixos-20.03.tar.gz) {};
      in { /*pkgs,*/... }: {
        hardware.opengl = {
          package = mkDrivers pkgs;
          package32 = mkDrivers pkgs.pkgsi686Linux;
        };
      }
    )
  ];
}

I'm on a Radeon RX 5600 (Navi 10) with amdgpu on 20.09 and I have the same issue with Trine 4 (what a coincidence!).
I'll play a few hours to test this (but the problem usually happens after about 1 min).

One thing to note, while @ajs124 is on X11 with KDE, I'm on Wayland with Sway, so I'm indirectly testing the patch on Wayland as well ;)

Well so… I wanted to say it all runs fine… until I chose to pick up a collectible letter I didn't have yet:

So you're probably fine unless you pick up letters (?)

Additional note: I really like how they incorperated my status bar and the rightmost part of my terminal into the game. Really gives me some good overview of my current PC state.

For anyone trying to reproduce this:
It was in Act II, The Thorny Hedge Maze at checkpoint 15 the first letter you find there.

Well, I'm mainly concerned about big regressions making desktop unusable, etc. If nothing like that happens, maintenance updates sound a good idea even if it doesn't (fully) fix the Trine 4 case. I don't have this version of Trine myself.

@dasJ can reproduce :'(

I'm on a RX580. This should still be merged IMHO, but more testing can't hurt.
The only other relevant GPU I have is an Intel iGPU, though.

How long do we want to wait for testers? Guess we only had amdgpu testers up to now. Unfortunately I'm on unstable with amdgpu as well.

I could also try an older Intel (Sandy Bridge, HD Graphics 3000), within a few days.

⬆️ I tried: desktop stuff, glxgears + glxinfo. I don't normally use this notebook, so no big testing.