"To address the common case of device loss or upgrade, a key feature enabled by passkeys is that the same private key can exist on multiple devices. This happens through platform-provided synchronization and backup."
Thus, unlike a FIDO2 key, you don't have to visit every online service to tell it about the new redundant keys you add.
The rest of the security article linked by madjam002 goes into detail how Google implements their version of that backup. It's a bit like Keybase in the sense that your other devices act as keys to unlock the backup for new devices.
Thus, unlike a FIDO2 key, you don't have to visit every online service to tell it about the new redundant keys you add.
The rest of the security article linked by madjam002 goes into detail how Google implements their version of that backup. It's a bit like Keybase in the sense that your other devices act as keys to unlock the backup for new devices.