And for the local TV and plex, the plex server tries to initialize a direct connection to the TV, the Android phone only acts as the connection initializer. However, the plex server is unable to connect to the TV, which is in a different subnet and no route to it exists, so it fails. So to be able to stream to the local TV from the Android client you have two options.
Mirror the phone screen onto the TV with Google Home app.
Download the movie etc. in the plex app, go to settings, sharing and enable advertise as server.