It's called "WinPE" or Windows Preinstallation Environment. It's very strange. Tools you really think would work like Powershell are completely absent by default, and when added work in unexpected ways.
Adding drivers is also painful, since it doesn't really support all of the regular windows drivers. To sideload drivers you have to do it twice, once for the install image and once for the winpe image.
*My knowledge of this stuff is about 7 years outdated, so it's possible they've improved it since then... Unlikely but possible.
https://en.wikipedia.org/wiki/Windows_Preinstallation_Enviro...
https://learn.microsoft.com/en-us/windows-hardware/manufactu...