Can't find Xlib.h despite having xorg.libX11 installed

Context: I am trying to build my own package in github actions, so I’m running the nixos/nix docker container. The following is true for both latest and master tags. This package depends on SDL2.

I am installing dependencies with the following command:

nix-env -iA nixpkgs.gnumake nixpkgs.gcc nixpkgs.gdb nixpkgs.patchelf nixpkgs.git nixpkgs.cmake

And compilation of my package fails with:

/nix/store/xdhh9yzkk2vw7dy2xnl8bgp20gdijj4y-SDL2-2.24.2-dev/include/SDL2/SDL_syswm.h:69:10: fatal error: X11/Xlib.h: No such file or directory
   69 | #include <X11/Xlib.h>
      |          ^~~~~~~~~~~~

I am not sure what could cause this since X11/Xlib.h is a part of the xorg.libX11 package, which is installed.

nix-env is not meant for installing libraries, use nix-shell. See also I installed a library but my compiler is not finding it. Why?