Nevermind! I solved it 
Turns out I needed to use the dev versions of the packages!
Leaving it here for future reference:
# .idx/dev.nix
{ pkgs, lib, ... }: {
channel = "unstable";
packages = (with pkgs; [
rustup
stdenv.cc
pkg-config
zstd
libxkbcommon
vulkan-loader
xorg.libX11
xorg.libXcursor
xorg.libXi
xorg.libXrandr
alsa-lib.dev
wayland.dev
udev.dev
]);
}