Radarr has the option to link the files when it imports them. Look in the settings
Use Hard links instead of Copy - Use Hard links when trying to copy files from torrents that are still being seeded
https://wiki.servarr.com/radarr/settings
https://trash-guides.info/Hardlinks/Hardlinks-and-Instant-Moves/
I've never managed to get it working. But I always have to do thing multiple times until it works.