It's possible to get the secret from the Steam mobile app. We can then use that secret to generate Steam specific OTP which includes letters. It is already supported in WinAuth (https://github.com/winauth/winauth), which is open-source, and copying the implementation can't be that hard. I would like to request support for Steam Guard OTP in 1Password apps.
1Password Version: Not Provided
Extension Version: Not Provided
OS Version: Not Provided
Sync Type: Not Provided