A 20% bottleneck like that indicates (to me) a system problem of some kind. 3dsmax is telling your computer to render something, but it's choking on some kind of bottleneck So, that means its lacking... something. That something can be power, size, memory, a valid location to render to, permission to write, etc.
Some places to start looking: (Some of these assume you built the machine yourself, if not, some may not matter.)
Do you have an built in GPU on your motherboard? Is it disabled in the BIOS? Maybe max is using the wrong GPU.
Is your system overheating? (Manual throttle by motherboard? You can test by taking the side off the computer, but it's no long term fix)
Does the problem happen if you run 3dsmax as administrator?
In your device manager, do you have an exclamation points?
Is your power supply big enough?
Before you installed windows, did you enable AHCI? (If you have an SSD?)
Is your RAM stable in that configuration? (If you built the machine yourself, not all RAM chips are compatible over a certain limit, typically 32GB. The motherboard manual will list the compatible RAM chips over a certain size.)
Did you install the drivers for the GPU?
Some articles with folks that have the same issue (with other software):
https://answers.microsoft.com/en-us/windows/forum/all/is-it-normal-for-system-to-use-around-20-of-my...
https://forums.tomshardware.com/threads/my-graphics-card-only-uses-25-no-matter-what-i-do.3809595/
https://linustechtips.com/topic/1401031-solved-low-cpu-and-gpu-utilization-in-some-games-but-not-oth...
https://graphicscardhub.com/low-gpu-usage/
Best Regards,
