Doh, totally forgot could easily split on the keyframes in MKVToolNix
Here’s an example of both Dolby Vision and HDR10+ in the same file, with fallback to regular HDR10. Any longer and the file was too big to attach…
X (2022) ~ DV and HDR10+ Example.zip (25.2 MB)
Plex doesn’t even see the HDR10+ part.