Thanks for your suggestion. There’s already another suggestion thread discussing an option for Plex to display more information in the Play Version modal, including if a video is available in Dolby Vision. Please comment/vote in that thread in order to help us avoid distracting or cannibalizing votes. Unless I’m missing some unique aspect of your suggestion I’ll close this thread as a duplicate.
Similarly there’s another suggestion asking for an option to distinguish different HDR formats incl. Dolby Vision details on the movie details page.