In reply to @lily:lily.flowers

doing a nixos config like the below should patch in the fix and then graft it into your system. it, uh, doesn't work in pure eval (e.g. flakes) so you'll need to add --impure or something if you use flakes (it also needs IFD, but unless you manually disabled that, it should be enabled):

system.replaceRuntimeDependencies = [
  ({
    original = pkgs.alsa-ucm-conf;
    replacement = pkgs.alsa-ucm-conf.overrideAttrs (oldAttrs: {
      patches = (oldAttrs.patches or []) ++ [
        (fetchpatch {
          name = "alsa-ucm-conf-splitpcm-device-argument-fix.patch";
          url = "https://github.com/alsa-project/alsa-ucm-conf/commit/b68aa52acdd2763fedad5eec0f435fbf43e5ccc6.patch";
          hash = "sha256-8WE4+uhi4W7cCSZYmL7uFpcHJ9muX09UkGXyZIpEd9I=";
        })
      ];
    });
  })
];