It smells like a CPU bottleneck, especially since upping the resolution and quality makes the GPU work harder. The harder the GPU is working, the less stress on the CPU.
The CPU utilization there is going to be deceiving as it's a 12 core part with 24 threads. I'd be surprised if that game uses more than 4 cores. It'll schedule the work across the cores, so they'll all get some utilization, but unless work is actually scheduled for more than 4 cores at a time, you're never going to max it out. 4/12 cores is suspiciously close to 30% total utilization.