It’s the other way around: RHEL is a corporate fork of Fedora.

Also, for people using some Readarr derivative with Hardcover metadata, how much of a pain is it to migrate from Goodreads to Hardcover (and is it worth it)?

Calibre-Web has always been interesting to me. Can it be deployed in such a way as to keep a Calibre content server also accessible? (e.g. for sync with the desktop app/Koreader/etc.)

Yeah, unfortunately. Apparently it was hell to maintain, especially the metadata server and all.