Since the log says
[FFmpeg] [INFO] [StripNALUnitsFilter] Stripping HDR10+ from bitstream
I think in your case you’re running into the issue where Plex can’t disable Dolby Vision on 4K Max when it’s profile 7.
And profile 7 FEL files also cause a black screen.
Maybe Dolby Vision should be stripped when the profile is not supported, and here HDR10+ would be kept.
