A lot depends on who owns the UK streaming rights for particular films.
The Disney Investor's Day Presentation suggested that Terminator: Dark Fate, Alita: Battle Angel, Deadpool 1&2, Logan, JoJo Rabbit, Parasite, The Planet Of The Apes Trilogy, The Kingsman films, Murder On The Orient Express and older films like the Alien franchise, The Sixth Sense, The Die Hard films, Con-Air and dozens of other catalogue titles will be available.
Many older tv series like LOST, Buffy The Vampire Slayer, Prison Break, The X-Files, Modern Family etc and the new shows available on Hulu in the USA that haven't aired here in the UK yet.
The Investor's Day presentation wasn't country specific though so it's hard to know which company owns which streaming rights in any particular country so some of the films mentioned above might not be available in the UK, and some films might be available here but not in Germany or Italy for example.
Hopefully, as many titles as possible will be available in 4K HDR. Disney+ UK's record so far concerning 4K as been a little iffy. There are a number of films that are 4K HDR in every other country that has Disney+ , that are only HD in the UK. The UK still have a huge number of films in 4K HDR though, so I'm hopeful for more under the Star brand.