Are you using SteamCMD Dedicated Server on a stand alone fresh install of Windows 10 ? If yes, you need to install the c++ run times from within the rfactor2/support folder now !!! edit: just realized, after your revelation that you actually have a stand alone server on the same lan network. Your port forwarding will be wrong. I need to see what the menu headings say on your picture.
It was the c++ run times. Very strange, I'm sure that all applications that I have installed until now, has always prompted med for the vcredist install if it was missing, but obviously not this program. Because of this, it would had been the last thing for me to try... Thanks!