I use Boox (the max and the poke) and they give you a QR code you can use to connect to the device and transfer files.

It’s a Chinese company and I’ve seen a bunch of claims that they don’t properly follow the licensing in terms of making source available, so there’s a layer of sketchiness there. If you can’t stomach Amazon you might not tolerate them either.

I deal with it because Android is that much more useful to me and the hardware and the UX modifications for e-ink are high quality, so I’m mentioning it despite your concerns. I wouldn’t be reading like classified documents on it or anything, but you’ll have to evaluate the tradeoffs yourself.