Apple TV 2026.20.0: Dolby Vision Profile 8 never starts — regression from 2026.19.1

I set up a Jellyfin mirror of my Plex server, had Claude handle the process automatically, and now use Rivulet on Apple TV to play my local Dolby Vision and 4K files. As a lifetime Plex user, I find their lack of communication unacceptable. Plex will become my backup for 1080p non DV files now.