A84
I don't believe any monster has blanket resistance or immunity to damage from nonmagical weapons. I believe they all say "bludgeoning, piercing, and slashing damage from nonmagical attacks" (emphasis mine).
Divine favor and Divine Smite do not make the attack magical. They deal additional damage that is radiant. That has no effect on the base weapon damage and its resistibility, but the additional damage is radiant and not bludgeoning, piercing, or slashing.
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