@bozon, try this:
“C:\Program Files (x86)\UiPath Studio\UiRobot.exe” /file: “C:\Users\testrobot\Documents\UiPath\Projects\StartFromCmd\Main.xaml”
The “file:” argument must be preceded by a slash (“/”), not a backslash (“\”). It’s easy enough to miss even if you stare at it for a while …
(This info is also in the link @Lucas.Pimenta provided)
Regards,
burque505