Can't get started on Mac. Asks me to scan code. Can't find setup code. App Store didn't send me app.

tldr:
The secret key is that long string in the emergency kit download.

If you've already set up the apps on your iphone & ipad, look for the key the logins. The 1password login will be at the end of the list.

the long version:

When the account was created, your browser generated a secret key and included it in the emergency kit.

The secret key is part of the account encryption & also recovers the account.
(It's like the recovery key on a mac encrypted with filevault..)

The password you set will open the apps for daily use.

Here's the 1password page for clear details on where to find the key.
https://support.1password.com/secret-key/