You should use Nettoplcsim in this way
- restart computer
- before starting any Siemens software, start Nettoplcsim with Admin rights, and let Nettoplcsim stop/start the Siemens service to capture the TCP port 102. Let Nettoplcsim in this state (open with no configuration)
- start Step 7 (or TIA Portal if you want to use this), then start Plcsim and download your project
- configure Plcsim station in Nettoplcsim, and start Nettoplcsim server
References
https://www.mesta-automation.com/nettoplcsim-how-to-connect-step-7-plc-sim-to-scadas/
http://nettoplcsim.sourceforge.net/
https://sourceforge.net/p/nettoplcsim/discussion/912717/thread/777cf7c4/?limit=25