I was just about to ask the same thing (about the "offline" partition)
I suspect that there is something wrong with that underlying installation that is not being expressed.
Now, that's how I called it and how I keep it.
About two years ago I started to become concerned with keeping my freedoms, and this included my digital freedoms.
At the time, I made a dual boot system with two Windowses - one offline and one online. However I broke my rules and I started to use the offline Windows for online tasks.
The next iteration at the beginning of this year was one large offline Windows host and internet thru VMWare VMs, such as Lubuntu for browsing tasks and Windows for online gaming.
This didn't work as well, as VMWare has trouble with graphics acceleration and sound on Windows machines.
I had to turn the internet on the Windows host, and even with browsing tasks delegated to Lubuntu VM, it still started to decay, just for simply being online, without any browsing activities.
I studied for two months what can be done with Linux, and the conclusion was that it was far too hard, needing too much work - including reformatting the large 3.9 TB partition - with results getting near to the limitations of a dual boot system.
Therefore I returned to the dual boot system with two Windowses - one for offline use and one for online use - but this time I can actually have online activities on the host via Lubuntu VM or Windows VM (if I want some downloads and not willing to reboot).
I managed to pack a Lubuntu 20.04 installation in 8 GB and it actually runs as a "qube". A batch file copies the VM to a Ramdisk and runs the VM from there. Should anything infect it, it has no effect - it is volatile. I took this as inspiration from Qube OS.
I can't do the same thing with the Windows VM. Even for my 64 GB system, it's too big of a nut.
The offline Windows one may need, time to time, to be online for a few seconds - say to add a new game to the Steam library - but basically it is to stay offline, and it feels really good how it works now.
Steam clients on both Windowses have been blocked from hosts, so that they cannot update themselves. Using the online Windows to update Steam games is actually really good. The Windows VM is bad at this task - internet thru passed thru dongles is like water thru a pipe with holes.
This is the best security arrangement I found. Notice that "security" in this context is not as much against online threats, but against policies moving us closer to the digital society. I am unwilling to get to the point to have an universal authenticator ("digital ID"), because the next step will be "on the right hand or the forehead". I want to be out by the time it happens.
Steam is basically my treasure. I have all my games there. Ubisoft said that "gamers have to become comfortable not owning their games". EA games can't even start without being online. I will certainly not be forced into an online-only model of life. When I will be completely off the grid - if, God willing, I manage it - I want to continue enjoying my digital content.
So that offline Windows is the one missing the COMSPEC variable.