Hitler being back after the events of Half Life 2: Episode 2 further confirms he was always an ¨administrator¨ of the Combine all along, they used their highly advanced tech to bring him back to the future right before the Soviets and the Allies caught him in Berlin and his new task is to rebuild Europe as the president of whatever nation was born in the long gone Germany and to help the Combine to come back another time against the rebuilt America and their sworn enemies: The Mantis Men made by Cave Johnson who now rule the entirety of North America thanks to their sophisticated negotiating skills and the Aperture Science tech they brought along after making a deal with GladOS in exchange of never revealing the true location of Aperture HQ.

This is why Valve has been holding back HL3 since Gabe can see the future through his 5th dimension Source Engine plugin on his Steam Deck that he found 25 years ago on his research of secret alien technology the Nazis found and hid in the Artic after fleeing to Argentina after losing WWII and upon failure trying to reverse engineer it because of the concern of his team of destroying the device by accident or causing a chain reaction that could actually bring the Combine to our reality but after long years of research they managed to make a lesser copy of the main key features of the original and successfully recreating another less powerful version that they are now selling as the Steam Deck we all already know today.