On latest version Plex beta on Chromecast with Google TV, problem is also with play Dolby Vision movie content. This play in HDR10…or is black screen. Few movies play in Dolby Vision.
My settings in Chromecast 4K with Google TV:
Chromecast Dynamic Range & Color format:
Dynamic range format preference: Dolby Vision
Match content dynamic range: Match content
Dolby Vision Mode: Low Latency