"If you use them via Windows, iOS, Android, or macOS, they are tied to the biometrics on your device."

There are no biometrics on my primary devices, which are desktop computers. No camera or fingerprint reader.

Your client device OS will not allow you to create a passkey without a local unlock PIN/password or biometric, and those local unlock methods do not traverse the Internet (they are handled with TPM/Secure Enclave).