It is available remotely, but only to you and the members of your Plex Home.
Friends will not get access to your TV tuner. This is an intentional restriction.
ok, so this is fixed now, thanks to your comment, I now understand that “friends” can be people outside your home and not just physically within the 4 walls of your house as I previously thought.
I setup new accounts under home users and those people can now access LTV&DVR from remote.