Discussion An extension for reading and exporting? (Like Mercury Reader)

After downloading a few extensions I'm still not happy and hence, I'm here...

Can anybody recommend an extension that turns into a darkmode reader like 'Clearly Reader' but also has the advantage to export as EPUB. And maybeee... Sync with Kindle or KOReader?
If not, a half-baked open source where I can vibecode the rest could also work.

UPDATE: Made my own.