Is there a difference between the lighting in the old VS. new office? I'm guessing that the new one has much worse quality LED lighting with less color rendering index / more flicker etc
Edit: oh wait, you mentioned the lights were off. Hmm…
A few ideas:
Possibly the roughness on the walls is causing some level of pattern glare (I have one window with blinds that go in a zig zag pattern, if I use my perfectly comfortable laptop in front of it I start getting strain)
Is the chair different? Chairs that easily move around too much or are at certain angles make me feel dizzy even if I'm looking at a good screen
Any smaller lights in the room like indicator LEDs on power strips etc.? Many times these flicker in a slow motion recording
or, that more glare on your screen in your previous office was actually helping you (that has never been the case for me but I've heard some people here like @async prefer glare)
or, the power outlet is creating interference that ends up affecting your monitor or screen (try running on battery to see what happens - - I'm suggesting this because there was one place I lived at where my lightbulbs would flicker every 30 minutes or so, but at other places nothing would happen, indicating the outlets there were working differently)
or, the side that the window is on matters (I can't stand when light only comes in from the left and start increasingly feeling more stressed out, but am perfectly fine when light is coming in from the right. A doctor I talked to once after tracking my eyes even verified that I was reacting very differently to when any light or sound happened on my left)
You also haven't done any Windows updates, correct?