A reMarkable ePub generator. This is essentially an open source version of Read on reMarkable. In contast to that extension, this will include images in the generated ePub files. It also offers more configuration options over the original extension — margins, text scale, line height, alignment, fonts, tags, and a cover page — available from the extension's options page.
Currently there's an unaffiliated hard fork that may suit your needs. Full support is planned