HDR10 and HDR10+ movies will not launch

[TheDreadPirate]

So the TV is running Roku OS, correct?

This movie is Dolby Vision 7.6. The only devices that support that are bluray players. Streaming devices will typically support DV 5 and DV 8. Plex is almost certainly transcoding the video, but it appears only the audio is being transcoded on Jellyfin.

Did you enable hardware acceleration and tone mapping in Jellyfin? Jellyfin does not auto-detect (yet) your system's capbilities so this has to be manually setup.

Also, there are settings in the Jellyfin for Roku app that tells the Roku to attempt to play videos even if it shouldn't be able to. I'm not at home to double check, but I'm looking at the code for the menu layout. In the Jellyfin app press the * menu button when on the Jellyfin home screen > Playback > Video Profile Level Support

And then disable "HEVC with the description "Attempt Direct Play for HEVC media with unsupported profile levels before falling back to transcoding if it fails."

You can also try * > Playback > Compatibility

And then disable "Disable HEVC" with the description "Disable the HEVC codec on this device. This may improve playback for some devices (ultra)."