I see thanks Robert. To cover all bases, let's try checking first if StartProcess is fully broken in your setup. Try running the first example in its documentation page,

https://reference.wolfram.com/language/ref/StartProcess.html

. If this is not working then the problem is likely well outside of the system modeling functionality and indicates a bigger issue in the Mathematica setup. If, on the other hand, StartProcess works, then you may be experiencing an issue with the setup of the compiler. Please follow the verification and configurations instructions here

https://reference.wolfram.com/language/tutorial/CompilerForSystemModeling.html

. If this seems fine, and simulation still does not work, then maybe some paths to relevant directories are broken. In that case please email us what the lines

WSMLink`Utilities`withDebug["Exe", SystemModelSimulate["HelloWorld"];]

and

WSMLink`Library`SimulationWorkingDirectoryOption[]

return.