Stuttering/jittering in VR mode with the Varjo Aero, RTX 4090 and 13900k cpu (solution found!)

I just don’t understand the whole VR settings business. I just did a complete reinstall of my PC (Windows, the works). All drivers and updates are in. I then set everything up exactly as I had it before (described above), and now my PC struggles to maintain 30 fps. I mean I just don’t get it, it’s exactly the same!