That option is only needed for a small handful of newznab indexers and also for if one add’s jackett as torznab in Prowlarr for a tracker that responds with magnet links.
Your issue is likely neither Radarr nor Sonarr nor Prowlarr, but an incorrectly configured reverse proxy
https://wiki.servarr.com/prowlarr/installation#nginx.
Also the *arrs and prowlarr should not be talking to each other via a reverse proxy if they’re all local or can otherwise talk via the LAN - it’s not needed, not best practice, adds a single point of failure, and adds a lot more complication that is easy to screw up. it’s like going outside your door to go in the back door to go in the kitchen…because you don’t want to just go through the hallway