I've seen several videos and stories on the internet where people cough into a petri dish through various masks to see which one works best. They then put the dishes in an incubator for long enough to see which on grows the most bacteria. The idea of course, is that we would want to breathe through the mask with the least amount of bacteria growth, and this would be the one that captured the most coronavirus. Preferably the mask that yielded the cleanest dish.
The problem here, is that these petri dishes are growing bacteria, not viruses. Conflating viruses with bacteria is very dangerous here, since our bodies evolved to eject harmful waste bacteria as far from our bodies as possible. When we look at these petri dishes that get nasty after awhile, the one that stops the most harmful waste bacteria from be inhaled off the inside of a mask is the dirtiest. The clean petri dish indicates that the harmful bacteria is still inside the mask and getting inhaled back into the lungs. The nastiest petri dish is the one that allowed your body to do what it was designed to do, and eject the most harmful waste bacteria.
The reason why masks accumulate this harmful waste bacteria that our bodies have rejected is because masks in the medical setting were designed to intercept bacteria. Medical facilities have had bacteria problems for decades, which is why masks have been worn since long before covid and mask culture dominated the political landscape.
Ok, in Europe, there's an EU Standard on facemasks where they can protect one another from bacteria. But the problem is, a virus can often be a thousand times smaller than bacteria, a facemask does not stop viruses. A mask is designed to stop/reduce droplets from a person's mouth and nose. If one huffs through a mask in the cold air, you can see the water vapour and obviously water vapour is much larger than a virus.
So because a mask reduces the size of the plume you breathe/cough out, it's deemed they offer "SOME" protection. So the experts logic is to wear a mask and keep 2 metres apart. The only trouble is, most shoppers in supermarkets shop much closer together than that because a mask gives you a false sense of security.
I asked my other half, she works in a mask factory, to get me a product sheet to see if they cover viruses. They don't, they just print on the packaging that they comply with EU Standard EN 14683, and that standard just covers bacteria.
So to sum up; masks do not stop the spread of viruses, they just offer some benefit by reducing your exhaled plume.