Take a look at my Feedback (https://feedbackassistant.apple.com/feedback/19626136) to see Apple's reply. They say this is expected behavior. I'll copy their reply here:
The numberpad is meant to be a text input acceleration if the user needs to input only digits, so it's initially presented when a user interacts with a text input view that is numeric.
However, the numberpad doesn't present other keyboard conveniences such as Autofill, or a Prediction bar, or any other extended features, beyond just the digits input. During feature development this was identified as a usability gap and engineering provide us with new designs to address those needs, we work around this by presenting the full software keyboard, if the user dismisses the numberpad and taps on the text input view again.
Topic:
UI Frameworks
SubTopic:
UIKit