I wanted to recommend Minisforum, as I have a um560, that is powered through usb-c. But that is not available anymore... So those kind of machines exist...
You could get a frame.work laptop in an external case, slightly larger than hand-sized, though.
In addition to minisforum, there is mele. Mele makes celeron based usb c powered mini pcs. Quite compact. Serves as a good thin client. And lightweight business pc.
Ideas are circulating in my head for a custom solution.
You could get a frame.work laptop in an external case, slightly larger than hand-sized, though.