Your master password will always be available for you to use to log in to LastPass instead of using passwordless login.
However, when you log in with your master password, you are still prompted to use your FIDO2 authenticator or the LastPass Authenticator app, at which point you can use the backup authentication method you set up (for example, SMS passcode, phone call, and so on) to complete the login process.
If you set it up beforehand, you can also use a YubiKey or biometrics (PIN on Windows or keychain password on macOS) to log in to LastPass.