Wolfenstein Youngblood God Key is a surprisingly mysterious item. As its name implies, it is an odd artifact that's actually been part of a wide variety of Wolfenstein games: a Da'at Yichud item that serves a very particular purpose. How to get it in Youngblood, then?
The God Key is very important in the Wolfenstein lore, and isn't just a simple upgrade item you get and then forget about in Youngblood. Quite the opposite, as it allows you to open the mysterious God Lock doors strewn across the game, as well as enabling a powerful new melee attack.
Wolfenstein Youngblood God Key
In the constraints of Wolfenstein's lore, the God Key is an interdimensional gateway opener, buth when it comes to practical gameplay purposes, it blasts open doors and blows enemies to pieces. The good news is that you'll receive your God Key abilities as part of Youngblood's normal story mode, so just keep shooting Nazis until Blackowicz himself gives you the Key during the very last mission.
When you have it, just go back to any of the God Key doors you found beforehand, and you'll enter what is essentially Wolfenstein: Youngblood's endgame content. This should work even while you're playing with a friend in CO-OP, from what we can tell.
Though not quite as narrative-heavy as its predecessors, Youngblood is still a crucial Wolfenstein entry for those who are interested in where this wacky story will go next. You can buy it on Steam and Bethesda.net, and there's cross-play enabled between these platforms.