Well this is what i get when launching steam from the terminal and then launching the game:

chdir "/home/ellie/.local/share/Steam/steamapps/common/Half-Life 2"
ERROR: ld.so: object '/home/ellie/.local/share/Steam/ubuntu12_32/gameoverlayrenderer.so' from LD_PRELOAD cannot be preloaded (wrong ELF class: ELFCLASS32): ignored.
ERROR: ld.so: object '/home/ellie/.local/share/Steam/ubuntu12_32/gameoverlayrenderer.so' from LD_PRELOAD cannot be preloaded (wrong ELF class: ELFCLASS32): ignored.
ERROR: ld.so: object '/home/ellie/.local/share/Steam/ubuntu12_64/gameoverlayrenderer.so' from LD_PRELOAD cannot be preloaded (wrong ELF class: ELFCLASS64): ignored.
ERROR: ld.so: object '/home/ellie/.local/share/Steam/ubuntu12_32/gameoverlayrenderer.so' from LD_PRELOAD cannot be preloaded (wrong ELF class: ELFCLASS32): ignored.
ERROR: ld.so: object '/home/ellie/.local/share/Steam/ubuntu12_32/gameoverlayrenderer.so' from LD_PRELOAD cannot be preloaded (wrong ELF class: ELFCLASS32): ignored.
Game Recording - would start recording game 220, but recording for this game is disabled
Adding process 44180 for gameID 220
pressure-vessel-wrap[44181]: W: Found more than one possible libdrm data directory from provider
pressure-vessel-wrap[44181]: W: "run/opengl-driver/share/drirc.d" is unlikely to appear in "/run/host"
pressure-vessel-wrap[44181]: W: "run/opengl-driver-32/share/drirc.d" is unlikely to appear in "/run/host"
pressure-vessel-wrap[44181]: W: Found more than one possible drirc.d data directory from provider
pid 44431 != 44427, skipping destruction (fork without exec?)
pid 44436 != 44427, skipping destruction (fork without exec?)
pid 44457 != 44427, skipping destruction (fork without exec?)

The way i configured it, is it fine tho?

hardware.graphics = {
  enable = true;
  enable32Bit = true;
  package = pkgs.mesa;
  package32 = pkgs.pkgsi686Linux.mesa;
  extraPackages = with pkgs; [
        vaapiVdpau
        libvdpau-va-gl
        libva
        vulkan-loader
        vulkan-validation-layers
      ];
  extraPackages32 = with pkgs; [
        vaapiVdpau
        libvdpau-va-gl
        libva
      ];
  };

hardware.graphics = {
  enable = true;
  enable32Bit = true;
};