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The tropes in this area get pretty specific as there may be distinctions between "doesn't use as a weapon" or "doesn't use it for any function whatsoever".
Ornamental Weapon - Completely unused weapons.
Weapon for Intimidation - Utilized for its intimidating nature, even though it's not used to actually harm.
Fight Scene Failure - A YMMV take, where there is an example for various Marvel animated series that mentions in relation to sharp weapon use, "Choose from the following for Wolverine's enemies: Mecha-Mook, No-Sell, Good Thing You Can Heal. Otherwise, Wolvie's gonna tackle someone." He can use his claws, but only against robots or targets that can't be (permanently) hurt.
There are other options, such as Set Swords to "Stun", where potentially lethal weapons are somehow very not.
Also Inverse Law of Utility and Lethality is the broader reason why swords in fiction are less useful than they should be.
I guess Ornamental Weapon is pretty close. I was thinking something more along the lines of the situation where the character has the weapon, is often regarded in-universe as someone who actually uses it, and there's no reason it wouldn't be effective, but they just don't see use, usually for some Doylist reason. I feel like I've Seen It a Million Times.
Edited by shigmiya64

Is there a trope for when a character has a sword, but never actually gets to use it? Usually for censorship reasons. Like Leonardo in Teenage Mutant Ninja Turtles, Sokka in Avatar: TLA, or Wolverine in the X-Men animated series (for a non-sword example).