[2022] What setting is creating lag spikes at 30% GPU utilization?

You’re right to suspect the CPU. This game is less GPU intensive and more CPU intensive than most. The voxel world is a big reason for that: the game has to do things like structural integrity and AI pathing calculations that would be easier with a static world. If you open the console with F1, several systems report how long their processes take. You could check the times reported to possibly narrow down what’s causing lag spikes.