If I sell my PS4 game disc and buy a digital version, can I still access my saved game?

Generally speaking, yes. Your save game will be compatible for both the physical and digital version of the game.

There is an exception, however.

Depending on the game, if the physical and digital versions are not of the same region, your save game might not work.

For example, Persona 5 (JPN) and Persona 5 (EU) are not compatible with each other.