Answer:
The calculation does use all the kernels. However, some processors support hyper-threading.
Hyper-threading is a technology that allows a single physical processor core to present itself to the operating system as two logical cores in order to improve processor utilization.
Some applications benefit from this and run faster. However, this is not the case for the computational kernel of RFEM 5. Therefore, the computational kernel of RFEM 5 often uses only the physically available cores, and Task Manager shows that the processor seems to have a usage of only 50%.