I am talking from experience here. Some of the documentation is out of date, some is meant for Channel NixOS installs and not so appropriate for Flake-based installs.
Most of the fixes for my issues I find across NixOS discourse forum posts, or in the subreddit of the other platform. The Wiki/official documentation is not enough.
I’m glad you switched to NixOS (welcome!) but this is gap in documentation is something that will become more apparent over time. The NixOS official wiki ironically often links to Arch wiki to explain certain concepts further.