What i did is, jailbreak [1] my Kindle Oasis, and install KOreader [2]. This gives you full access to upload whatever ebook you want (SSH, WebDav, Syncthing, ...) and it can fetch RSS feeds (i use it with FreshRSS.) PS. The (very old) Kindle Oasis is still the best device there is to read on in my opion. Which is crazy, since it was released from 2016-2019... It has 2 phyisical buttons to turn the page, and an ambien…
Or, even better, don't buy a Kindle in the first place but get something that doesn't need a jailbreak, like for instance literally any Kobo reader.
I've had my Kobo Clara HD for almost 8 years and I still use it daily with KOReader. It's so easy to install KOReader and it's really repairable. I replaced the SD card at one point, and another time I thought it was broken or needed a new battery but came back to life after reseating cables.
Before that I had a kindle and you had to jump through a lot of hoops to install KOreader, and I remember you had to be careful not to upgrade the firmware so it could be jailbroken.
Like I said I've had the Kobo for 8 years, so I hope this is still the case.