https://www.cnet.com/news/fallout-76s-beta-will-launch-first-on-xbox-one/

If you want to be part of Fallout 76's upcoming beta, you have to pre-order the game. We knew that already but here's what we didn't know until now: the Fallout 76 beta will launch first on the Xbox One.

As per the Fallout 76 beta FAQ: