USB tethering from an old smartphone should work fine. Just make sure your carrier allows it and you have a decent data plan. Could be a cheap option if you've got an old phone lying around.
so about this ram upgrade - did you have to do any trace modding/reball anything or did you find chips that fit the existing pads? overclocking potential with the better thermals?
if you're looking for a portable gaming pc that can handle most games decently, the steam deck is a solid pick. good balance of power and portability, plus steamOS works great. only downside is the high cost, but you get what you pay for.