I like foliate, certainly one of the slicker options out there, but yes it does have the behaviour you describe.

I do have need of a library, but there's not much point for me if it's just one or two types of document. I've just moved to the new Zotero 7 beta, which has epub support, has always managed PDFs and web snapshots, and since Zotero 6 has supported rich annotation.

Perfect setup for me. One library containing all my notes, citations and reading.