Newsletter content for fiction authors

I have two pending names, one for fiction and one for non-fiction. My non-fiction newsletter is going great and I have no problem with content.

But I haven't developed my fiction newsletter list. I wrote one tech thriller and have in mind some historical fiction mysteries going forward. But I struggle to think what newsletter content would interest fiction readers. Should I post pics and info from vacations, hobbies, etc? I suppose the super fans might be interested. Buy that feels like social media feed

What have other fiction writers used? And have you done it in a way that has regular newsletters without stressing you out to post the next newsletter and not let it lapse?