The “studies” which say that masks don’t help are taking rigid view of the situation. If one person gets sick while wearing a mask, they say masks don’t work. But the problem with studies like that is that they assume every mask is the same regardless of what it is made of and they all provide the same level of protection regardless of how properly the person is wearing it. They don’t consider that different mask materials offer different levels of protection. They don’t consider that if a mask has wide gaps on the edges it will provide less protection. They also don’t consider that masks will lower transmission within a population. Just because masks don’t bring transmission down to zero doesn’t mean they don’t work. If transmission goes from 50% to 25% when masks are introduced, then masks drop the transmission by half even though some people still got it. And even if you get infected, masks will lessen the initial viral load which tends to lessen the severity of the infection. The studies that say masks don’t work are defining “don’t work” as meaning “bringing the transmission rate to zero”.
This kind of fallacy would be like saying all body armor doesn’t work because one person died while wearing body armor. There are different kinds of body armor and different kinds of projectiles, and different combinations will provide different levels protection. And even if the armor fails, it will have mitigated the projectile to some degree which may lessen the injuries the person receives. But there is no body armor which is 100% perfect and someone may die regardless of what body armor they are wearing.