It is really stupid.
If you are talking about on the TV app on the phone, Mac et., then the shared libraries of films, series etc., are still there in iTunes.
If you aren't familiar with this you have to go to 'purchased' and select the family member of the person that bought them.
The family manager may also have to set up sharing again under Catalina if you've upgraded (I seem to remember having to do that).
Once you've started to watch it on your device it will appear in the TV app.
Otherwise, you have to know what's already shared and when you navigate to it, it'll let you play it rather than telling you to buy it.
I think it's really badly implemented but the whole app is a bit of a mess at the moment in my opinion.
And how that works out on the actual TV I don't know. I haven't got to other family purchases on that yet.