Tired of Fast thrillers, any slow mysteries?

I’m looking for a book with some mystery but not the usual fast-paced, high-suspense kind. I want something slower and a bit more layered or thoughtful. No fantasy, and no or very little romance. I’d also prefer a younger protagonist. I liked Little Monsters by Kara Thomas. I also enjoyed Pony by R.J. Palacio. It's not a mystery but I loved the way it was written and how the story unfolded. Even after reading mainly YA thrillers that rely on “what’s going to happen?” to keep you hooked, I didn't find it hard to get into at all.

(I do enjoy the thrillers too but it's not something I feel like reading rn)