If unpatched for the PS5, games designed only for the PS4 will run on the PS5's PS4 legacy mode, whereas games designed for the PS4 and Pro will run on the PS5's PS4 Pro legacy mode.
Some games won't work, although that seems to be a vanishingly small amount, judging by the recent "99% compatibility" statement.
Any PS4 games released after June/July this year have to be natively compatible with the PS5, as per Sony's terms. Given the gulf in CPU and GPU power between the PS4 Pro and PS5, you can safely expect the PS5-native version of post-June/July PS4 games to play at 60fps, as that's the most straightforward way to take advantage of the greater than doubled clockspeeds
And maybe this someone else will listen. You've been relentlessly bleating on about this matter no matter what you're told. Is this your new "16 Jaguar cores"? Can we expect 2 years of you going on about this in spite of the preponderance of evidence and well informed opinions around you?
It depends on what Sony's done though, in terms of backwards compatible features in their APU design. We certainly saw a bunch of patents pertaining to the likes of spoofing clocks.
So if Sony are able to make the game code think it sees a GCN GPU, we may see performance improvements akin to running non-Pro-enhanced games on the PS4 Pro with boost mode turned on. Which isn't exactly something to be excited about, because it didn't really do much of anything...
I remember being quite excited at the possibility of Bloodborne's frame pacing being solved by boost mode... no such luck [emoji3525] So I really hope Sony have invested some resources in getting it to run properly on the PS5, given its presence in the PS+ Collection.