Hello nimvio! 👋
On the iPhone AutoFill is specifically handled by iOS through an Apple technology named iOS Password AutoFill and 1Password only provides the data for the experience. Password AutoFill will match the apps that you use to your login items in 1Password by taking the associated domain associated with an app and comparing it against the website URLs in your Login items. If there is a match then Password AutoFill will offer to fill your login information.
If your Login item is not being suggested for a particular app then you'll need to add the app's associated domain to your login item in 1Password. The associated domain can be found underneath the Create Login button that appears when you tap on an app's username or password field and then tap on the Password AutoFill prompt above your keyboard.
In your case I see that there is no website address underneath the Create Login button. What this usually means is that the app's developer hasn't set an associated domain and you'll need to search for the Login item (as you mentioned doing) in order to fill your login information.
Let me know if that helps. 😊
