Is this book yet another horror?
Hello! This is not a horror, no. It's very much in the vein of BOOKS & BONE, the novel world it is based on -- a fantasy with a necromancy aesthetic but more taking the world of necromancy as if it was normal, and much more focused on relationships. If you would define BOOKS & BONE or my other books as horror, though, then you are unlikely to enjoy MAKING FRIENDS.
I will say however that MAKING FRIENDS is by far grimmer than any of the other Tombtown stories, so judging by your question it is probably not what you're looking for.