How to save passkey for existing login

Hi there, I updated to 1pw8 after happily using 1pw6 for many years... solely to use passkeys. :)

I now need to update an existing saved login to add a passkey, but the site is not in your directory – probably because it's a feature available only to employees of my organization.

I looked over the instructions and not seeing how to add a passkey manually – either for an existing or new login:

To save a passkey, find an existing login that now supports passkeys using Watchtower or create a new account on a passkey-supported website. Depending on the website, you may need to create an account with a username and password before you can create a passkey.

When you choose the option to create a passkey, 1Password will offer to save it. If you have an existing Login item for the website saved in 1Password, you can choose to update it by adding the passkey. Or you can save the passkey as a new item.

"When you choose the option to create a passkey" - where is this option? Is it never shown if the site is not in your directory?

Furthermore... I just looked in Watchtower and I see no indicators of any sites in my vault that support passkeys, even though there definitely are some, like Github. "Check for passkeys" is checked off in settings.

Thanks!

1Password Version: 8.10.20
Extension Version: Not Provided
OS Version: macOS 12.16
Browser: Not Provided