When will passkey support be introduced to 1Password on iOS?

Github, you enter both username and password, then click "Use security key" on next page. It's more like 2FA in this instance.

Try this:

https://github.com/login?passkey=true

That will enable you to log in via a passkey without entering username/password first.

(This is a temporary solution until their passkey support moves out of beta)