Combining the most recent posts by @Bep and @jimhami42, you might conclude that it would be better to consider a gas filled void rather than a vacuum.
Kingspan’s VIPs have a declared R value of 0.007. Impressive but that may be for the panels themselves rather than a whole roof (say). That is because you cannot cover the whole area with butted VIPs.
Xenon has a R value of 0.005. This is a gas that is used in high spec glazing (not to mention headlights) and has one of the lowest R values of any material, barring perhaps the latest aerogels.
Whilst you could in theory conceive of a double skinned shell made of metal (say) with a gas-filled cavity, the challenge then would be getting sufficient rigidity, especially when fitting other components like windows and doors. Appliances like fridges and freezers are presumably made a bit like this but with something like a urethane foam insulation core.