Dont let people here discourage you...they are totally ignoring the Brownian motion. btw, masks are one area that engineers and MD’s may not see eye to eye and one reason why you see such a varied opinion about masks. Although, I am sure there are plenty of engineers not wearing masks.
The goal for mask wearing really boils down to lessening the viral load. Sure, some will get through...the less that get through the better chance the body has to fight it
this is an interesting graphic of virus movement and masks
https://www.nytimes.com/interactive/2020/10/30/science/wear-mask-covid-particles-ul.html
With a 99% survivability/recovery rate, who cares about face masks.