Backports work because the 13.4 firmware (or whatever wolverine needs) has been exploited. The encryption keys that are part of 13.4 have been dumped and extracted using that exploit, so now you can tell your 4.0 ps5 to tell Wolverine to "decrypt the game with this key" and it'll do it. If GTA needs 14.0 keys, you won't be able to do that until someone cracks 14.0 and dumps the key. You could give GTA the v13.4 keys just like Wolverine, but GTA doesn't decrypt with 13.4 keys.

Similarly, pirates can create decrypted dumps of games (I don't know about ps5 but definitely on other consoles) by passing the key through during the dump process. That still requires having the key though, and getting the key means exploiting the firmware that distributes that key.