This question is about the Armorer artificer's Armor Model feature. The description of the Guardian armor model's Thunder Gauntlets says (TCoE, p. 16):
Thunder Gauntlets. Each of the armor's gauntlets counts as a simple melee weapon while you aren't holding anything in it, and it deals 1d8 thunder damage on a hit. A creature hit by the gauntlet has disadvantage on attack rolls against targets other than you until the start of your next turn, as the armor magically emits a distracting pulse when the creature attacks someone else.
Can you wield a shield (or weapon) with one gauntlet, and still make the special attack with your other hand? Or do I need both gauntlets free to do this?