I have a product labeled Boogieboard that I bought on a whim at Costco years back. I want to say it was less that $10? Really simple, no connectivity, it does really seem like an etch-a-sketch with a stylus instead of knobs. Stuck it on the fridge with tacky-tack and it’s been going strong for many years. About the size of A5 (or half an 8-1/2 x 11 piece of paper).

EDIT: looking at the link above, it is called the Jot and sells for $18. Still made apparently.

I have a couple boogie boards, and they're very handy for making notes or single-session scribbles, but their major drawback is the "all or nothing" reset.

I don't think I realized how often I need to erase or update a small section of a list or diagram without erasing the entire thing until using these.