Do I need Norton Protection on my iPhone 12

Johnathan Burger above is correct. No.

Nor do you need an add-in VPN client. (Which is basically what the app you’re considering is.)

(Fun fact: an add-on security app cannot scan your iPhone storage. iOS blocks that.)

You do want robust and unique passwords, and two-factor authentication enabled, and you will want to review and probably resolve any password recommendations listed in Settings > Passwords > Security Recommendations.

No.

iPhones are already pretty secure. I don’t reckon.