Yes, all versions of the PS4 can play Blu-ray discs, but not if they're 4K — here's what you need to know

The PlayStation 4 and PS4 Pro can play Blu-ray discs, but not if they're 4K UHD Blu-rays. The standard PlayStation 5 can play all Blu-rays.
Game Rant

Inserting PS5 Discs into PS4 May Jam Disc Drive

A few curious gamers who own a PlayStation 4 and a PlayStation 5 disc have discovered that the two should not mix. This results in the PS5 disc being jammed in the PS4 disc drive, requiring a tricky ...

How to play PlayStation 4 games on a PlayStation 5

You can play PlayStation 4 games on a PlayStation 5 because the PlayStation 5 is backward compatible with the PlayStation 4.