PS2 base models were BC to PS1
PS3 base models were BC to PS2 (and PS1) even before they added digital-purchased emulated copies.
PS Vita has a built-in PSP that can play digital versions of those games as well as PS2 ones.
PS4 had a very limited selection of PS2 games released digitally for it.
PS5 is BC with PS4.
They could do a lot better, though. Their digital offerings are extremely limited and have yet to tackle the issue of emulating the cell processor at reasonable speeds.
100%.
I know this is a thread for someone new, but perhaps as a future fix: I grabbed a mini PC to do plex transcoding and all of Plex’s content is on a separate NAS with a 14TB RAID. I think the mini PC has 500GB by default