Right now to cast media from Plex to a Chromecast enabled device you need to call the play media service with a specific Plex url (since v0.117).
You can use the Media Browser to select content from Plex when you’ve casted to a certain device at least once but this will duplicate each cast device in the player selector and also will only work when Plex was casted at least once since the last restart of Home Assistant.
What I’m hoping for is a way to select Plex media in the media browser for a cast device similar to how the Media Source integration works.
I’ve just had a short look at the code and as far as I can tell it would require a new MediaSource implementation for plex?
There doesn’t seem to be a way to limit a MediaSource to certain MediaPlayerEntity implementations so the Plex source doesn’t show up for unsupported devices. Is there a way to limit the media sources shown for a certain player?