While it took all of the Avengers and the death of Iron Man to stop Thanos from snapping his fingers once more in Avengers: Endgame, Conner Kent's Superboy could have stopped the Mad Titan with one finger. Thanks to his dynamic and unique powers as a clone of Superman, Conner Kent wouldn't have broken a sweat attempting to recover the Infinity Stones, using his tactile telekinesis to save the day in the MCU.
In Avengers: Endgame, the Avengers assembled against the armies of Thanos, resulting in a major battle that saw the new gauntlet and the Infinity Stones Earth's Mightiest Heroes had collected throughout time changing several hands. While the heroes' goal was to get the gauntlet away from Thanos before he could destroy the entire universe, the Mad Titan eventually got his hands on the Stones. He would've then snapped his fingers to end his conflict with the Avengers once and for all, though Iron Man succeeded in taking them using his suit's nano-tech, sacrificing himself in the process to erase Thanos and his forces from existence.
However, Conner Kent's Superboy from the DC Universe could have ended the fight before it had even begun. In the Reign of the Supermen arc, Cadmus Labs created a clone of the original Superman who would be known as Superboy. However, they were unable to replicate the powers of Kal-El. Instead, Superboy was given a telekinetic force field around his body to mimic Superman's flight, speed, and strength. Furthermore, Conner was also able to manipulate the field and affect his surroundings by touch, resulting in a unique power that's referred to as tactile telekinesis. As such, Conner could have achieved the same results as Iron Man by simply placing a finger on the gauntlet to eject the Stones from the guantlet.
Combined with his artificial strength and speed, Superboy would have likely have been able to keep Thanos from snapping his fingers again during the final battle with very little effort. While not every version of Conner Kent has tactile telekinesis, it's certainly a unique power for a superhero to have all things considered. Additionally, Superboy could have just dismantled the entire gauntlet by touching it if he wanted in the same way he could instantly disassemble a car by placing a hand on it.
In any case, despite Superboy's tactile telekinesis being such a particular (and downright weird) power, it actually ends up being perfect for the type of scenario Iron Man was in with Thanos in the fourth Avengers film. Superboy could have prevented the snap meant to end the MCU no problem, and the Mad Titan would have likely been beside himself in surprise had the unique DC hero been involved.