As a reader, I think they're generally a waste of time. They can be helpful, for example, if you knew that you were going on hiatus for an extended period of time or pulling the story for some reason or another. Life happens. However, I mostly have seen them as mini-journal entries from the writer: whether begging readers to go subscribe, follow them on their socials, or add further insights on the chapter. *To me, this last one is incredibly frustrating because if I need a long author's note to explain plot points or give more insight on world building, you didn't do your job well.
However, if the author's notes ADD to the story like Lemony Snicket, for example. Go for it. Aside from A Series of Unfortunate Events, I know of a couple other series where the author writes themselves into the work as another character and it's brilliant.