Similar situation here, 4090, 5800X3D, OpenXR, DCS MT Standalone.
Limiting FPS in OpenXR Toolkit will absolutely stop the 'shakes', but I need to lower it to around 40-50fps (where FPS counter shows CPU bound instead of GPU bound) to reliably stop the glitching. As you bump that number up it gradually gets worse.
Looks to be a few other threads around MT CPU Bound/Bottlenecking, so hopefully it's on the radar!