There are 2 million keys being given out in different batches. You must make an account and link it with Steam.
There are issues making new accounts, but if you already have one then it should be easy. This is the studio behind Dead by Daylight.
Game Summary: What the Fog?! You’ve been sucked into a cursed boardgame! Now you and a friend will need to work together to survive. Run, jump, dash, and shoot to escape swarms of angry monsters in this chaotic co-op roguelite from the world of Dead by Daylight.
https://account.bhvr.com/account/my-account/games/what-the-fog