I use an iPad with a keyboard when I need this kind of “writing room” thing, but I know someone who uses an ancient electronic typewriter.
FWIW when my disorganisation is catastrophic, I go out for a walk, leave my phone at home if I can, sit on a bench, and try to organise my life in one side of A4. And then if there’s a task that I can start by writing, I do it there, with a pen.
I fairly frequently leave my phone in the office and take a clipboard full of lined paper and a ballpoint to a place where I can write without access to the internet - I've got a number of published CS papers and at least one funded grant where a significant amount of writing was done in longhand on paper.
Of course this would require a bit of software work and maybe a brain swap to make it into the sort of portable typewriter that I'm really looking for, but given this as a starting point it should be fairly easy.
One question I have - what is the finished weight?
Caveat: such a device should not be infested with shitty spyware like everything else these days.
The closest modern device is the Planet Computers PDA, which can run Linux, but it can’t run mainline Linux and it has a modern color screen that uses too much power.
This is the 21st century version of an axiom: it's an XKCD.
Pairing is a pain, charging is a nuisance, battery life is a constant worry, responsiveness is dodgy... there is nothing good about it. Give me something built-in, cabled, and always-on.
Wireless is for fashion victims.
It's fun to push old hardware to the limits and develop software/hw for it (such us wifi for apple 2 from 1979 hehe)
Clunky hardware has one advantage too: It's usually a single tasking tool. Great for focus and running away from WWW.
Your kid can play pac-man and Tetris without fear of popups, credit cards, scams, hate and porn.
Really: you could lock me into a room with just a pencil and a ream of blank sheets, and nothing of value would come out, and that's not because of the technology or the distractions, but just... well...