This would let the user know all the sites in their vault that support passkeys but where they haven’t yet enabled one.
Similar to how we have 2FA warnings on sites that support 2FA, when we do not have 2FA enabled, have a feature to show which sites support Passkeys when we do not have them enabled for that login.
In the reports section on the web, next in inactive two-step login, there should be an option to show passkeys that are available but not in your vault