Funny. I just raised this point a week ago, at work.
I asked a co-worker (who was wearing a mask) if they could still smell anything while wearing it. (the subject of farts and shit particles was brought up too). Long story short, they COULD smell farts and the like and thus we concluded that any mask that can't block fart particles is not likely going to block the Corona, either.
Most masks stop you from spreading the virus, not contracting it.
I know that is the claim.
Where is the "real world" evidence / proof?
When I cough or sneeze hard, I feel like I could push a grapefruit through the mesh of a screen door. Let alone a particle as small as the coronavirus through a less than optimum mask.