Yes, that is what I meant, I always had problems with it. Iirc Android uses the mtp protocol for file transfer, it is not like accessing external storage. Before I can read / write files to the phone's storage I have to perform some steps on the phone's UI (this already rules out doing this while the phone is off); the exact steps changed between android versions. And then if I manage to remember, not all files and directories are visible.

With a pocketbook, you connect it and it is like you attached a USB stick.

Gotcha. Yeah, you get a notification from which you can swap mode. Default being charging only, for security reasons.

Also, android encrypts the filesystem by default these days I believe. So unpowered fs access is a no go without a lot of work for a very niche use case.

Security doesn't really matter on a somewhat dumb e-reader though, so seems like sensible defaults for the respective devices tbh.