I don't own a PS5, I do own a PS4 however and still buy physical copies of games - some of which of late have been secondhand from CeX - because 1. I don't like renting content, 2. I hate DRM, 3. physical copies are harder to censor.
Sony recently expunged copies of movies people had bought, so I honestly don't trust them not to do the same with games.
Also, they announced the closure of the PS3 store, so that's even less reason to trust that I won't be able to reobtain the games I've bought digitally in the future...
Actually, thinking about this now, I tried to play PS1 games on my PSP about two years ago, but couldn't because they needed to be (re-)authenticated.
Sadly, there's NO way to authenticate PS1/PSP games on PSP anymore. Even connecting it to the PS3 via USB and trying to authenticate it didn't work.
(At least PS1 games still work on PS3 for now, though.)
Though you have a physical copy of the game, I don't discount a future where a console refuses to load a physical copy of the game because DRM impedes it. Much like when short-lived TLS certificates expire on their own, even by being offline.
Physical copies of games have in their EULA that the game is licensed to you, so theoretically they could still disable it.
Precedent? BlackBerry phones refused to connect to WiFi if you didn't pay for your mobile data plan. It became a 2G brick.