It should say that somewhere in the ad (in the US) or the garage/unconditioned space is omitted entirely even if it is a 24x24 or something. It might get a separate mention though depending on who is selling.
It’s bonkers, but it varies regionally in the US on how a garage space is treated. Midwest? You park a car in there out of the snow/elements. Southeast? It’s for all the junk you don’t want in the house.
With budget pre builts, you’re usually sacrificing performance to an extent of cheap power supplys (that can blow up) and a tier or two lesser graphics unit for the same price as you would building it yourself.
Honestly, if you’re happy with the performance the steam deck provides then you should stick with that long enough to either realize your need for a purpose built desktop, or put it in a gen 2 steam deck down the road.