I read a number of Project Gutenberg books on my Palm Pilot in the late 1990s. 160x160 monochrome.
To beat that you'd pretty much need to read a book off of one of these: https://www.newark.com/lumex/lcm-s01602dtr-a/dot-matrix-lcd-...
Now, I'm sure someone is either A: going to pop up to claim that they did or B: pop up to say they now have their next Arduino project. "E-Readers are so big and expensive, so I thought I'd roll my own with parts I just have lying around..."
Anyhow, when I see people talking about they can't possibly code with anything less than a 4K display, I still find myself chuckling a bit. Not that they're bad things by any means, but... well... it's a pretty big leap over where I started. I remember the excitement I had in college when I could get 800x600 and 1024x768 for the first times. So much text!