It answers the question, but does not gives the solution :)

I mean, shouldn't that be the point of unattended access? I got some rendering machines which I occasionally need to supervise, but they're clientless and headless without keyboard or a monitor, so jumping in the active Windows session is pretty much impossible. And hence no users on the machine, just the local Administrator account (set without password).

I found a loophole - set TeamViewer on the remote machine too, so I just join with Teamviewer to see the PIN and click on "full control", but that's kinda making security even worse (if you're talking about security).

Can't there be a single "full control anytime password without PIN" set somewhere and let it just work as it should? :)