@oliverhviid1 Hello there! I'm sorry to hear you're having trouble launching Assassin's Creed Valhalla.
You should not need an activation key with a game purchased from Epic Games.
As a first step, can you please log out of both the Ubisoft and Epic clients, log back in, and attempt to launch the game again?
If that does not resolve your issue, please try the steps below:
Please note that both the Epic Games launcher and Ubisoft Connect client should be run with administrator rights when performing these steps.
1. Close the Epic Games Launcher.
2. Go to your system tray, at the bottom right side of your screen.
3. Find the Epic Games Launcher icon and right-click the icon.
4. Select Exit from the menu that appears.
5. Go back to the system tray and check if the Ubisoft Connect logo is there.
6. If it is, right-click the logo. Select Quit from the menu that appears.
7. Lastly, restart the Epic Games Launcher and launch your Ubisoft game.
Once this is complete, your game should no longer ask you for a key and you can start playing.