Does anyone know if there any way to do this (eg: using something like Tailscale to get the remote device - in my case, an AppleTV - to appear locally on my network) but just for the Plex app?
Create a smart collection, which e.g. uses a sharing label to filter items.
Publish this collection to the home page, just for them.
Then add a sharing label to the item you want them to see.
When they look at the Home page next time they’ll see it – front and center.
Collections can only be created by the server owner.
If these are smart collections, you can select in their properties whether they shall be using the “watched” state of the server owner or the shared user.