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.
Hope is all we can have. Sadly time and time again there were companies who thought the were smarter than others and altered established protocols. Be it Telegram or OAuth with Facebook. But let us hope.