lol i already jailbroke my 2012 paperwhite and intstalled Koreader on it so I can sync it with my calibre epub library over wifi

It's a pity Calibre to date refuses to be refactored into a self-hosted service. The core logic should be portable, with the app just being an interface to it, but no, the entire project is so much spaghetti it would feed the entire boot for over a year... such a shame.

I switched. Kavita is the new hotness.

I found it for comics, but realized it handled books as well as Caliber does, in a modern interface with OPDS support.

I tried Kavita and immediately recoiled at the fact that basic features like progress sync or metadata matching are behind a paywall - literally features that don't cost the developers anything, while having open, active bug reports going back a year on these "premium" features. All while licensing the code under GPLv3...

Progress sync works fine for me in KOReader with OPDS. Progress Sync Scrobble (to third-parties) is the Kavita+ feature. My understanding was the Kavita+ items are things to do with third-party services and meta data providers that are an API/cost-based service to the dev. That being said I don't use any of those features.

OPDS doesn't do progress sync, at all... you're running something else there if that works for you.

https://anansi-project.github.io/docs/opds-pse/specs/v1.2 They use the PS extension. I believe Komga and Kavita maintain the spec now. Reader support for Kavita specifically is in the Wiki.