I have experience with driver circuitry for waveshare e-ink displays and ARM H7 which has USB2 and Wifi. It shouldn't be too difficult to build a small device w

I have experience with driver circuitry for waveshare e-ink displays and ARM H7 which has USB2 and Wifi. It shouldn't be too difficult to build a small device which is powered by an USB power bank, receives from a USB keyboard and communicates with a USB LTE stick. So I'm pretty sure that someone has already designed something similar as open hardware that you could fork and customize. I'd start with Googling "kicad eink arm". From memory, the Watchy eink watch with esp32 comes to mind. And I think there are arduino epaper driver boards on Amazon, too.