With my CPU (AMD Ryzen 7 2700X) it says that one CPU (CPU 3) is used to 100%, but I don't know why and that is only the case in minecraft. What should I do and is that normal?
It all depends on what you have, lots of plugins, lots of redstone, water, lava, bad configurations, errors and not enough RAM. Anything can be decisive for a 100% utilization.