I've played the OpenDev scenario on Stadia and have repeatedly tried to break up the army of two scouts that you start with, but clicking on one of the scouts in the army and them on the button to split him off or transfer him to another army does nothing.  It's possible that I'm just not understanding how to do it properly, but if that's the case, then merging and splitting up armies needs to be covered in the tutorial at release because it's going to be critical for players to form effective armies.