@rune you'd be jealous of the ones we have in Switzerland. No weighting or whatever shenanigans. You just scan you stuff.

And because the whole system relies instead 100% on the honour system, that means you can get a hand scanner at the entrance, scan while you shop and already pack everything in you groceries bag. At exit you just dock back the scanner and pay, while your groceries stay in the bag.

There's even an app on the smartphone instead of needing a scanner.

@patricksh for Linux, do check #SailfishOS, imho the most mature option. Jolla now sells hardware with (would recommend that), it can also be bought and installed on select phone (some Sony Xperias), and there is a community edition.
(my daily driver is a Xperia 10iii).

Tiny tablet combo: that's the way several Linux phone are setup - the phone part is an isolated USB modem.

(am typing this reply literally on such tiny tablet: a PinePhone Pro running a community edition of SailfishOS)