Stop using Chrome! Download the Brave Browser via >>> [Brave.com]
It's a forked version of Chrome with native ad-blockers and Google's spyware stripped out! Download for Mac, Windows, Android, and Linux!
You want to point to /mnt/unionfs. If you don't want radarr/sonarr to rescan, just edit the container and add a mapping in container /path/to/media/that/radarr/uses to on host /mnt/unionfs/path/to/media