Yes, physical PS4 game discs will play on PS5. You'll be able to insert physical PS4 game discs into the PS5 and play them, as well as download digital software you've purchased from the PlayStation Store. Note that you won't be able to use physical game discs on the PS5 Digital Edition (See Also: PS5 Digital Edition vs PS5: What's the Difference?), as it doesn't have a disc drive.
The information that the PS5 can play 99% of the PS4 games reinforces the idea that Sony intends to take 4 thousand games from the current generation to the new. It is worth mentioning that who will decide