Kobo has ways around it. Especially if you manage to get certain models. - certain variants have the entire Linux based OS installed on its SD card - you can remove it to edit the internal sqlite database with an SQL editor to bypass the login requirements. Other models are supposed to have methods to just not use a login. (Though I've never been successful at that)

Also, to save battery it usually doesn't connect to the internet unless you tell it too (sync update or whatever)

I have the Kobo Sage, while it doesn't have a removable SD card, and I did have to create an account initially. It doesn't require you to use it - you can plug it into a PC and just copy any ebooks, cbz comic files or PDFs you want to read. But I chose it for one reason: it's one of the most stable models for running KoReader, a custom interface that adds some interesting features. Including support for direct OTA syncing with the Calibre eBook management and editing software. All Kobo devices has a hidden folder that can be used with a koboroot archive file to flash stuff into the internal file system.

Running this software literally kills the original interface, (meaning it can't spy on you) and gives you full root access via an inbuilt terminal emulator. The fact it gives you access to full internal storage, means you can retroactively bypass the account requirement system, as their operating systems are almost completely identical across models.

Before that I used to own an old Clara HD (the screen broke, highly advise buying a cover for any e-reader) and did the SD card trick to bypass login.

There's a huge community for hacking most models of eReaders for better and more uniqur experiences. Theyre low security ARM devices, way easier to mess around with than an android phone these days. All Kobo devices have single account Linux distros - meaning everything is running as root.