Second camera in editor causes flicker/judder/lag in VR image.

I'm using SteamVR plugin. When I add a new 'game view' window and set it to anything other than 'Display 1', even if there is no camera rendering to it, I get a strange judder in the image on my connected head-mounted display (Quest 2). Its appears as if every other frame is missing (or amplifying) the rotational time-warp, so as you rotate your head the image splits into double vision. It does not seem to be a performance issue, as even without a rendering camera, the issue persists. When you change focus to another window, like the Inspector, the problem goes away.

The EXACT same problem as in this unanswered question.

https://answers.unity.com/questions/1515848/vive-performance-hit-when-adding-a-second-non-vr-d.html

I want to use the second game window to capture footage for a VR game, with a second camera in the scene taking different angled shots. But the game makes me sick to play with the judder behaviour with the second game view open!