Hi @czmenz,
If you have splashtop WiredX display or Duet display driver installed on your primary machine, please uninstall then reboot your primary machine before connecting a spacedesk viewer app.
For more info, please check “Incompatible Display Hook Driver Detected” chapter in our user manual https://spacedesk.net/user-manual/.
Follow-up- if you have splashtop WiredX display, there’s an Advance option in their settings window, make sure to uninstall the Virtual display driver there, then you can use spacedesk after that.