Define and use NixOS module options within a flake.parts flake

Hello, I’m reading about flake.parts and co for a while now and today I tried to setup a basic flake with utility commands for the shell and by now I’m more confused than convinced (very confused). I started with a template and added packages (what worked). Then I tried to add nixosModules with options and config, like I previously did in a normal flake. But, the new options aren’t accessible from the config part so my configuration can’t react to eventual settings from the user. I tried mult...