Voadam
Legend
Generally the rules are designed to match some cool fiction then turned into cool generally applicable game mechanics, they are not just bald game mechanics divorced from any fictions.This still comes down to making the fiction bend to the rules, rather than the opposite; which is a fundamental problem for some.
That this fiction-bending is here put on the player's plate doesn't change what it is.
The difference of making up narration to fit or bending the rules for the situation only comes up in corner cases against not typical situations.
My instinct is to apply the RAW fairly strictly and make narration work where I can, but be flexible on unwritten narrative stuff. So if magic missile says target creature then I envision a Shadowrun mana type mechanic that attacks the animating force of a living being, a spirit, a construct, or an undead, but does nothing against inaminate objects like a lock. If I can narratively conceive of a blow knocking an ooze prone and imposing the prone condition on it which it is not immune to, I go with it. When a 5e PC asks whether heat metal can target a metal construct monster or PC warforged, something not directly covered as far as I can tell, I say sure, but their melee attacks and grappling are burning hot as well.