A Horror writer looking for some actually scary but grounded horror ideas! <3

I feel like working with paranoia in some way could be a great place to start! Maybe a character is constantly paranoid something will get them but it's never there, or a person/group of people are super paranoid due to a specific thing? (manipulative pastor, shared trauma, pseudo-science theory crafting, etc.)

you could also look at other pieces of media for inspiration or base parts of the story your trying to tell on real things (deep sea diving, mountain climbing, or abandoned buisnesses just to name a few)

One simple way to easily portray true horrors of many is to dive into common phobias, even uncommon ones and try making them into the true horrors of the person experiencing them. Write about things that almost starts feeling physical in the reader, like drowning, getting stuck in a cave, being chased, hunted, choking on something horrible, etc. There are endless ways to portray horror, make it realistic and possible.