I’ve had nothing but issues trying to build Qt 6 with Nix.  Currently, CMake will detect some of the libraries I denoted in my derivation, but many won’t be picked up.  I’m using https://doc.qt.io/qt-6/linux-requirements.html and trial and error with the CMake test output to determine which libraries should be included.  This is what my derivation looks like:  let   unstable = import (fetchTarball https://nixos.org/channels/nixos-unstable/nixexprs.tar.xz) {}; in {   pkgs ? import <nixpkgs> {},  ...