Every time Passkeys comes up, I think it's important to point out it takes the FIDO dongle model where a private key that never left the device, is now is passed into the hands of either Google or Apple for management.
I mean I totally understand how it could be easier to use and manage, but it just kind of scares me.
I don't think it's quite right to say they never leave your device.
The page you linked says:
"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."
I mean I totally understand how it could be easier to use and manage, but it just kind of scares me.