https://wccftech.com/dont-expect-your-ps4-saves-to-work-on-playstation-5/

The jump from one console generation to the next hasn’t been a very straightforward process for Sony, even long before the announcement of the PlayStation 5. PlayStation 1 to 2 was perhaps the smoothest transition, with games, accessories and saved data all working on the black Y2K monolith. The transition from PS2 to PS3 was a bit more messy; only the Emotion Engine-enabled launch console had complete compatibility for both previous generations and if you wanted your PS2 memory card to work, that was a completely separate accessory to purchase. Playing your PS3 games on PS4 was almost non-existent. Your main options were the PS2-on-PS4 software lineup that Sony supported for a couple of years (including releasing some RPG gems like Rogue Galaxy and Wild ARMs 3) and the PS3 lineup is limited to whatever is currently offered on PlayStation Now.

With Microsoft pushing its backwards compatibility message harder than its next generation offerings, some are looking to Sony to see what their answer is to the question that’s on more gamers’ minds this console generation than the last: how will I be able to play my games on next gen?