Hi all.
Right now, there isn't a central list anywhere online of websites which use passkeys that we could use.
We rely on https://2fa.directory/ to show websites that support two-factor authentication, and although we use it to recommend two-factor authentication-capable accounts in Watchtower, the list is maintained by the "2factorauth" group on GitHub: https://github.com/2factorauth
There may well be other similar lists out there online, and there's unlikely to ever be a single source of truth for it, but this is the one that powers things with 1Password.
Passkeys are still very new, and nowhere near as widespread as two-factor authentication, either as a sign-in method on websites, or as something that users are currently using to sign in. Even without such a list, the passkey experience as it stands today is very limited, so the risk of missing out on it (so to speak) is still quite small. We're aware that early adopters will be at the forefront of using passkeys wherever and whenever they can, but since passkeys aren't yet supported in 1Password, having a list of passkey-enabled websites might be a little premature at this stage.
We're going to continue to be a leading voice in the development of passkeys, and in particular, their adoption by users. We're continuing to look at what we can do to help with that as things develop.