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Ben, et al, my issue was not related to Butterfield's "no beta ver installed". It was installed.

I got this to work, not by using iOS Mail, but but taking the link above
https://support.1password.com/cs/passkeys/#step-1-create-a-new-account-with-a-passkey

and opening it with iOS Safari (I normally use iOS Chrome). This opened correctly in iOS 1Password at the "Set up your account" dialogue. I was able to successfully create a new account with a different email address and save a passkey. I created a secure note as a test.

For fun, I went to my MacBook, with 1Password for Mac 8.10.9 (81009045) and went to Manage Accounts, and was able to login to my new account by authenticating from my phone and making the MacBook a trusted device. Nice!

I saw that the new passkey was stored in my iOS Passwords. I then went to Safari on MacOS and tried to login with my new account at my.1Password.com and as expected, it wanted to unlock with a passkey. When I told it to, it popped up a dialog with a 6 char code? I canceled, and found the 1Password app open. But in Safari, it showed "Unable to sign in with passkey". After quitting 1Password and trying again, it fails to open with a passkey and 1P doesn't open. Maybe the beta isn't this far along yet?

What I don't understand is whether the new account/vault is protected by a Secret Key? Is my main/original 1Password account the "parent" of this new account?