This thinking that a computer needs to be connected to internet to be infiltrated is not rooted in reality.
Why do you think in certain areas (meetings) there are NO CELLPHONES allowed. Because even if the SIM CARD is taken out and the phone is turned off, World intelligence agencies have ways to turn it back on and gain a signal. That is why Osama Bin laden had zero cellphones near him while hiding in Pakistan and his carriers did not use their cellphones unless they were far away from his location.
So this notion that if your cut off form internet then you are “safe” is borderline naive IMO. If that were the case then the Chinese wouldn’t be able to hack into the top secert mainframes of the Pentagon all the way from China.