I have A LOT of digital purchases on the PlayStation Store. This has been a result of me moving from place to place and not wanting to carry numerous discs with me. Updates are a huge anyway and I have started treating my console software collections in a similar way to my Steam library.
Sony have stated in a post (linked below), that over 4000 games will be playable on the PS5, some benefiting from enhancements. This is most likely limited to framerate unless developers issue substantial patches. At that point they would probably start selling new editions of the game.
There are a few exceptions but nothing to be missed and the PS5 may show some unexpected errors. In my view, it's fair and I will rarely going back to my PS4 collection. It's just nice to have it there.
support.playstation.com/s/article/backward-compatibility?language=en_US&lan