I faced the same issue, but I wanted to use my Kindle to read RSS feeds without relying on my PC, phone or Amazon, so I built a FOSS web-based RSS reader compatible with the Kindle browser. It may make your life a lot simpler.
Link: https://inkfeed.xyz Repo: https://github.com/adhamsalama/inkfeed-reader
Interesting project! I’d love to self-host but can’t find the backend server code - could you share a link to its repo?
I discovered this post while reading Hacker News on my Kindle BTW.