While Silent Hills' P.T. was briefly reported to be playable on the PlayStation 5, that was before publisher Konami yanked it from the console. It was previously believed that the demo could be played on PS5 via wi-fi transfer, and it sounds like that indeed was the case.
P.T. has been unavailable to download since early 2015 when Konami cancelled the Silent Hill reboot following a public fallout with designer Hideo Kojima. Since then, anyone who has wanted to experience the demo for themselves has been unsuccessful (unless they paid for a hard drive already containing the game). However, since players who still had the demo downloaded are still able to play it, there was a belief that the game could be played on the upcoming PlayStation 5 through some form of backwards compatibility.
As GamesRadar reports, this indeed was the case at one point, but not anymore. According to GamesRadar, "The PS5 did initially let you transfer PT from your PS4 and play it on the new console. Until you couldn't. I know because I did it, and played it, on a PlayStation 5. However, if you try to repeat the process now you get the message during the transfer process that[,] 'you can't use this game or app on the PS5'."
As for why this was this case, GamesRadar added, "Konami has gone on record as saying PT won’t be backwards compatible with the PS5 via a PlayStation Store download, but the fact that I was able to transfer and play it initially suggests this may have been a conscious decision, rather than a lack of support. The option was possible and has been taken away."
The article also reports that as of October 27th (the date the above screenshot was taken), P.T. could be played without issue, but support for the demo was removed without warning. Fans of the demo have been trying to find ways to experience it again, such as with the help of mods recreated in DOOM's engine. Yet, it seems like Konami is continuing to make sure that that does not happen.
While Kojima has long since departed Konami, started his own studio, and even voiced his desire to work with Junge Ito on a project one day, Konami is still holding on to the Silent Hill IP, but not doing anything with it (nothing that we know of, anyway). It is truly a disappointment that a beloved franchise with a passionate and dedicated fanbase is being held up for mysterious reasons (although, fans looking for a Silent Hills fix might be interested in the newly released Visage).
Source: GamesRadar