I am a bit worried that the standards and ability to move around is not just part of the implantation right out the gate.
I do worry what this will mean for the more average user, this is a major shift in how things work.
Passkeys used to be called non-resident keys.
In the world of hardware security keys there was no backup/share of private keys.
In this new wave of software authenticators (typically backed by the hw coprocessor that’s now available in phones & laptops), they called them passkeys, added sharing across devices, and a few debatable features like interactions with servers that may lead to lock in/tracking/etc (or may not).
Passkeys is more or less just a more convenient implementation of FIDO2 or the like, as you'd traditionally have with a Yubikey token. Instead you move it to a supported password manager or mobile device.
If you want to try it out go to https://passkeys.io on your Android or iOS device. I do believe Passage is more or less what Passkeys is/already was.