Comment by barnabee
The Onyx Boox readers have a feature called BooxDrop which runs a web server on the device when you enable it that provides file management and upload. It simple, wireless, and works great.
The readers work perfectly fine without an account and the Poke 5 I have is a fair bit smaller than the last Kindle I had with the same size screen.
It runs Android and I also use Termux plus a bluetooth keyboard with it for a rather nice minimal writing experience.
I've been tempted by their products in the past, but unless they've improved their stance on their use of GPL covered code in a non-compliant manner I don't want to support their business.