That might be your intent to use multiple files, but your entire config as it currently stands is not referencing any other files, and trying to rebuild with this should give you an error about some options not being set.
If you’re using other files, they need to be added to the modules attribute in the attrset that’s passed to lib.nixosSystem.
But unless this is your first day using NixOS, you already should have a config that works, if you followed the installation instructions in the NixOS manual. So I’m asking what the contents of that working config are.