What is the support of Microsoft about unsigned drivers? They support a System with them?
I'm looking for a document with the Windows Policy support and what they said about not drivers.
You would need to ask Microsoft about the specific case in hand.
While I've not had this issue with drivers, my experience has been that they will support a system up to the point where it becomes certain (or at least very highly likely) that the problem area is the unsupported area, at which case it becomes your problem to move back to a supported configuration and to try and reproduce the issue.
Seems reasonable to me.
Signed drivers are only needed to meet the requirements of the Windows Logo Program and the Windows Hardware Compatibility List. That's it. There are NO support requirements regarding signed drivers. Microsoft will support their OS regardless of which drivers you're using. If they determine the driver is the issue, then their support responsibilities end there.