From PS Blog:
Please note that the ability to transfer game saves between a PS4 version and a PS5 version of the same game is a developer decision, and will vary title by title for cross-generational games.
For Marvel's Spider-Man: Miles Morales, when players decide to upgrade from PS4 to PS5 their game saves will transfer.* Sackboy: A Big Adventure also will support game save transfers from PS4 to PS5 in an update that will be delivered shortly after the release of the game.* We'll share additional details on both games closer to launch.
PS4 games on PS5: Your top questions answered
Details on backward compatibility, how Game Boost enhances select PS4 titles, and more.
blog.playstation.com