Passkey is some sort of specific unique key to a device allowing to use a pin on a device instead of the password. But which won't work on another device.
Now I don't know if that key can be stolen or not, or if it's really more secure or not, as people have really unsecure pins.
Kinda. Given that nobody else supported it Google dropping it did sort of kill it. Passkeys are very different as they are already supported by Apple, Microsoft, and scads of smaller companies.