While everybody was celebrating in the Bat Cave, Luke and Selina got into the police car and returned to their roles as police officers to maintain order in Manhattan.
As for their whereabouts in this battle, Luke had already come up with a solution.
The Thousand Faces System and a couple of robots that completely imitated their physiques weren't good enough yet to not come across as strange when interacting with people, but in today's chaos, they were enough to fool the outside world.
The enemy they had encountered this time was an alien army. The soldiers' mechanical bodies were very resistant to bullets; even shooting them seven or eight times with a pistol might not work. Only a rifle could just barely break through their defenses.
Coupled with the fact that the other party basically had control over the battlefield, it was normal for Luke and Selina not to perform spectacularly.
