Why the Old Methods Fail
If you search for “install Sonarr on Linux,” you’ll find plenty of guides telling you to add a repo, install Mono, and call it a day. On Raspbian, that advice is outdated and mostly broken.
I hit this wall myself. The traditional Sonarr install steps that work on Ubuntu or Debian-based servers either fail outright or leave you with a non-functional service on Raspberry Pi. This article documents what actually works on Raspbian today.