While Sony has yet to give a definitive answer to the question of the PlayStation 5 console’s backward compatibility with PlayStation 4 games, a past statement from the company tells us that all or nearly all games will work fine.
However, it turned out that there is still a nuance. The games themselves will work, but your saves in these games will not be transferred to the PS5. That is, it will not work to start playing on the consoles of the current generation and continue on the consoles of the next one.
While there is speculation that, perhaps, the save can still be transferred through the cloud storage through a PlayStation Plus subscription, but there is no confirmation of this.
It is unlikely that this feature will stop many from buying, but a situation may arise when it is easier to finish playing this or that game on PS4. By the way, Xbox Series X / S won’t have this problem.