As to whether you can still transfer your already downloaded P.T. from your PS4 to PS5 via physical storage and whether or not it's backwards compatible is not yet known. The same for the other exploits to download it again.
Sadly, my P.T. copy got deleted from my system from what I suspect was a firmware update...
Someone on ERA did some checking, and it seems that the PS5 website's backward compatibility interface that returns a positive result for P.T.
Just to put this not compatible theory to rest, the new https://library.playstation.com/ web site has an API which it is accessing to determine the backwards compatibility state of a game. You can see the requests it makes if you have the developer panel open in your browser.
Anyway if you put in one of the IDs used for P.T it returns a compatible result:
And to verify it's actually working as intended, if you put the ID of a known incompatible title like Hitman Go it returns not compatible:
So P.T is very much playable on the PS5 through BC as long as you have it on your PS4 and can transfer it.
Now are things being just identified as compatible unless they're specifically confirmed not compatible? If that's the case then they probably just aren't going to check PT since it won't be downloadable anyway. If it's the other way around and things are only being added as compatible if they're confirmed to work then that's interesting.
There's probably some automated process that they use to check thousands of games. Especially on PSN, so P.T. might've just automatically got listed in there.
So by default, the majority of things may be listed as 'working.' And P.T. and many things are more likely to work than not.
In fact I suspect that even the games that are known not to work, likely don't due to licensing issues rather than technical ones and could be specifically prevented from doing so, but there's no way to prove that.
That said, even if it is listed as working, doesn't mean there couldn't be emulation issues.
So basically only the shortlist of games Sony has officially confirmed to work and not work are guaranteed. We won't know until we try.
