Here’s the actual settings in Sonarr.
As Sonarr imports, directories get 755, files get 644, which is exactly what you want.
The find / chmod command you show is correct.
The chown should be such that your UID owns the files.
This results in plex having Read-only access to the media every time.
One problem you do have is the /media
directory.
If this is a HDD mounted by the automounter, Plex will NOT have any access.
Automounts are exclusive to your user id.
You must mount somewhere else to avoid conflict.
This is the documentation I wrote