Full BC yes but you can Expect only a few titles will be compatible from the Start! Also they will find a way to charge money for that feature, where ms will provide it for free.
Ripping of the customers is there business model &philosophy
You will get full BC with PS4 and it will be without patches.
If you have to issue a patch to a game it will require new or existing licences to be renegotiated. For example, think of car or music licences in Gran Turismo. The term of the licence would likely include the game platform and an expiry date.
All of these would be invalid on the PS5. No one is renegotiating anything like that. The rights owner may have changed or a million other reasons why you don't want to open that can of worms. They will likely want more money for one!
So you will get patchless, free, works for all BC as standard.
The recent patent shows exactly how they expect to handle this without human intervention/patching. Offline a BC program will determine the best BC config for every title and then only each config is required for any title on the PS5. New titles can easily be added prior to release as part of the TRC process.