When it comes to an eBook reader, the choices are limited. The market is dominated by Amazon’s proprietary Kindle along with a few other options like Kobo, Nook and Onyx.
An interesting news for open source enthusiasts is that a developer, Joey Castillo, is working on creating an open
reMarkable is also a good device, very light and you can enable SSH/root access with a simple toggle on settings. There are also entire repositories of software for it https://toltec-dev.org/ https://github.com/Evidlo/remarkable_entware