Ah you are right - I had created the Proton Doc on the web and launched it after from Android after. I did not actually create the file in Android. Just checked and the option is not there for me either. Maybe next update? Still would prefer the ability to use Standard Notes as the client, similar to how I can with SimpleLogin today.
Yes - you can use your Proton account to log directly into Simplelogin via web, browser extension, or Android app. I suspect the Proton Pass feature is related to their partnership with Simplelogin but not sure? I actually just noticed the email generation Pass feature this week. Having that integrated into the password manager is really handy. May be time to start using it but migrating password managers is a pain.