The Radarr Linux install instructions contain an incorrect piece of information critical to the setup.
The instructions state "Ensure ownership of the binary directory." by using sudo chown radarr:radarr -R /opt/Radarr.
Just above these instructions it states that it is assuming the user will be "radarr" and the group "media".
The proper instructions should state sudo chown radarr:media -R /opt/Radarr otherwise it will likely fail due to a missing "radarr" group.
https://wiki.servarr.com/radarr/installation/linux