I just want to throw out that you might like Kavita for a comic/book server. It's built to feel like Plex. https://www.kavitareader.com/

I do agree that Plex doesn't seem like a good fit for books and comics. The first major hurdle is the lack of a singular metadata source that Plex can hook into for metadata - although this year has shifted with Hardcover and MangaBaka. Plex also uses a filename parsing mechanism (like Kavita does) which has drawbacks since books and comics have an extremely wide variety of naming conventions and lack of good tooling.