KeePassXC has support for passkeys now. However I've only managed to make it work with GitHub. Bitwarden does not work for now (although their passkey implementation for log-in is reportedly in beta).

Not sure what your password manager is, but 1Password supports them and its a pretty smooth experience.

The idea of a passkey is that it's bound to a device, and you can have more than one passkey. Think of a YubiKey, just that you can use your Phone or your PC instead. You basically have designated hardware that is always allowed to just login to your account...