To expand on that (for those who might not know), the actual secrets are physically on the Yubikey and the Authenticator app on iOS or Android is using them to

To expand on that (for those who might not know), the actual secrets are physically on the Yubikey and the Authenticator app on iOS or Android is using them to generate the One-Time Password. This means you can also roam those secrets to different devices (as they are on the Yubikey). But it also means that you need to have access to the key whenever you need the OTP! One caveat is that you can "only" have 32 or 64 accounts per Yubikey (number depending on the version of the key)