Auth Server is not proscriptive about how an organization authenticates a person. If you want to avoid passwords, that's great. Everyone knows passwords are terrible.
Modern authentication flows use a series of web pages to mitigate sufficient risk, enabling them to issue an assertion about the subject's identity. In order to perform authentication, identification is a given. This implies that all authentication flows normally start with the subject asserting some kind of identifier: username, email address, phone number, or any other identifier that uniquely identifies a person. Auth Server is not opinionated about how you do this. You could prompt the user to enter their identifier. Or for example, you could ask the user to scan a QR code, and identify a phone identified with a person.
With identification done, Auth Server can present any number of additional web pages to establish that identity. These pages can ask for any "factors". For example, if you want to perform two factor authentication in one step, you could use a FIDO 2 credential, which combines possession with either knowledge or biometric. But in practice, you could ask for any one or more combination of credentials--none of which must include password.
Net-net, "passwordless" is really just marketing jargon. Normally it implies some kind of risk assessment to optimize user experience. If you can imagine any such authentication flow, you can implement it in Auth Server.