I'm sure they exist but I have yet to come across a service that both removes the ability to also use a password when you register a passkey and also has no other recovery methods if your passkey (and/or password) become unknown or unavailable to you

In theory if I locked down my Apple account with the advanced protection features that are optional, I could lock myself out, but it would be on me to save recovery codes/secondary passkeys/etc during enrollment in those optional configurations

Otherwise, I'd walk into the Apple Store and they'd be able to get me back in my account if I didn't have some alternate method to get in