Thanks for the question — we've forwarded this to the product team as feedback.
We suspect you've already done this, but just to rule it out: could you double-check the following setting on your device?
Settings → Personal data → Passwords → Settings → "Autofill in other apps"
It should be enabled with Norton Password Manager selected as the autofill service. If that's already set and Norton still doesn't surface its prompt inside Opera, please let us know — that would help the team narrow down whether it's a real gap.
Thanks again for the feedback.