Does Webots use at most one core of the CPU

I found that when I open multiple Webots, the maximum CPU utilization of each Webots in FAST mode is about 100. I want to know if each Webots uses up to 1 core of the CPU.

By default, Webots uses a single core. In the WorldInfo node, there is an optimalThreadCount parameter which you can increase to use multiple cores. However, please carefully read the parameter description as it will not necessarily speed up the simulation.