A demo clip isn't the best example—demo clips are almost universally single-layer, and we know that the Apple TV 4K can play them in MrMC and Infuse (latest betas only, but this is at least a working solution). I just tested an untouched .m2ts file direct from the UHD disc of Spider-Man Homecoming. Mediainfo verifies that this m2ts has a 1080p DV layer separate from the 2160p HDR10 track. LibreELEC (MINIX NEO U9-H, Amlogic S912) ignores the DV layer and sends an HDR10 stream to my display (Vizio P75 with Dolby Vision).
Oh really... so it doesn't activate the Dolby Vision for you hmmm.. I really am wondering how some users made it work then....
Thanks for testing this!