KOReader is my jam! With its reflow for PDFs, I've used it on my Kindle Oasis 2 to read everything for my undergrad and graduate degree. Some years ago now, I wrote a script that converts the annotations to Obsidian [0], and then another little script to automatically keep my "Articles" folders in sync between the Kindle and my laptop.

Very grateful for this software!

[0]: https://github.com/simonpacis/kohico