Security Writer 
Valve: “We need a credit card on file to prove you’re 18”
Me: “My account is 23 years old”
Valve: “That just proves your account is old”
Me: “A credit card just proves you know someone with a credit card”
Ok this is interesting.
The desktop app has no such restrictions, only mobile.
Mike Siegel@SecurityWriter my favorite is apps that offer webauthn features on their mobile app, but desktop doesn't offer 2FA? Da fuq? Do they have an actual fucking potato doing their threat modeling?