I really enjoyed both The Witch and The Lighthouse. Odd films, if you're into gore-porn, these ain't the ones for you. More focused on building tension and mystery, much like The Wicker Man or the first Alien film.
First four Alien films are good, classic blend of sci-fi/horror. If you like sci-fi, you definitely need to watch at least the first two films.
The Shining is a mainstay classic of course, wife and I watch it every October. Stanley Kubrick was a master of his art medium.
Event Horizon (for those who can stomach gore) is good, I could only view it while almost blacked out on etizolam lol. Good blend of sci-fi/horror as well.
And though not a film, Twin Peaks is a fantastic Fall classic. You either like it or you don't, I can't even describe it well. Fans of David Lynch stuff should like it, especially Fire Walk With Me and The Return (season 3).
I don't think any of those are on streaming services at the moment, I just have them all on hardcopy. Twin Peaks might be on Netflix for just the first two seasons, the rest is probably on HBO Max. The Lighthouse might be on Prime, it was last month.
Edit: Oh, The Thing (1982) is also a good October flick. Classic alien horror style with a unique twist. Also not on any streaming services I know of, I watched it on my friend's Vudu account.