Questions optimizing ArchVis for VR

Development Architectural and Design Visualization
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I would have posted this in a VR section had I seen one but it is related to Architecture as well.
I have been going through online tutorials talking about how to optimize for VR. Unfortunately many of the biggest recommendations are ones I would prefer to avoid which is making it challenging.
I have been getting into playing with Cesium which as far as I can tell isn’t designed to work with static lighting.
I would also love to have the possibility of incorporating a day cycle, or maybe sliders to choose different times and day of the year.
Because of this ideally I would like to stay with Lumen and dynamic lighting.

I have one main question that is more VR specific.
I have a Vive Cosmos and Vive Pro 2.
When I open a project in desktop mode it utilizes a lot of CPU and GPU. When I go into VR mode the performance crashes but so does CPU and GPU usage.
All resources say that VR needs a lot of setting tweaks and reduction because it is so resource intensive but what resource is the bottleneck? Why does CPU and GPU drop so much lower in VR?
A while back I posted on the Steam forums because Real Flight 9.5 was doing something similar. CPU and GPU use dropped in VR and graphics go to garbage while the Steam VR performance graph goes off the charts.
In that thread the assumption was that their game engine was only utilizing one core of my dual 10 core Xeon processors. being high core count the clock isn’t super high so single core it’s not great.

I have watched core useage and none seem to be maxed in my Unreal projects though. So why isn’t it better able to utilize CPU and GPU?

Also if anyone has any settings recommendations I would love to see what you have found works. I have probably 4 tabs pulled up with different recommendations but some are different than others.

I found next to no difference comparing anti-aliasing settings, forward shading, volumetric fog, or instanced stereo. Though I have deleted fog, and set to recommended settings.
All testing and comparing so far has been done in lumen though. Do I really need to switch to static lighting and baking? If so can I make that work with Cesium?

Still seems ridiculous trying to mess with settings when my computer is just idling in VR.

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I just noticed something really interesting.

In most cases including in Real Flight both task manager and CPUID GPU utilization are reading close to the same value.

In my project displayed on my monitor with my headset on and at Steam Home Task Manager is reporting 85% GPU while CPUID is reporting 98%.

Switching to VR in my project now Task Manager show GPU usage at 8% but CPUID shows it at 85%.

I wonder what is causing that disparity?

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Type ‘stat unit’ into the console. That gives you some basic information about CPU and GPU usage. Anything red is being considered too high. VR requires 90 fps which is a lot more than the 30 fps that are needed for normal scenes. So if ‘frame’ (render) is already red than it means it is too high for 30 fps. Get the fps with ‘stat fps’.

Also you may need to disable or change ‘smooth framerate’ or similar worded. That’s a project setting that tries to balance frame rate to a certain rate. I think default is 60 fps which may limit your framerate to that value.