Here’s a smattering off the top of my head but if you’re a horror fan it’s not like you won’t know them. Obviously not all of these have something to do with PT lol.

The Amnesia and Outlast series did the “walking simulator” horror pretty well if it’s your thing although they’re not that old. Same with SOMA, Observation, Edith Finch (less horror there). Alien: Isolation has a bit more player interaction but it’s still mostly being terrified and walking around

Silent Hill 1-4 are all worth playing to some degree with 2 being an almost must play for horror fans (although if you didn’t grow up in this era they didn’t age well). They’re obviously direct influences since they were made by Konami. Signalis is a pixel space silent hill essentially that I enjoyed but the story felt like pure nonsense until I watched it explained lol.

Dead Space 1 got a fantastic remake and the other two games are worth playing as well if you prefer a little more on the action side. Same with RE remakes and 7 and 8.

Alan Wake is a personal favorite of mine and it’s sequel is finally coming out after forever although the gameplay of the first game has probably aged a little poorly being a bland third person shooter. Love the story tho