I can confirm this issue is still active and have the same experience as that user.
When I enable “synced content” under “sharing” setting for my iphone, other devices can discover my device, but there’s no library there. It just shows up like an empty server with no folders for movies or tv.
My use case is to pull synced content from my iphone to play on my ipad on a flight because the iphone has a lot more storage capacity then my ipad does for media.
If I am understanding this right, this basically makes your iphone act as a local plex server and you can stream content from it to your ipad or other devices.
It would be a pretty helpful feature because I’d like to watch some movies on a bigger screen.