Icons does not appear
You have to install a compatible icon theme. For example, you can install the
adwaita-icon-theme available as
gnome3.adwaita-icon-theme in Nixpkgs.
Vulkan not found on startup
You can ignore the warning as it is just cosmetic.
Epic Game Store
If you're running a 64bit environment you need to ensure that you enable 32bit support in your
hardware.opengl.driSupport32Bit = true