I find it extraordinary that someone would think that the efficacy of masks is thought to be extraordinary. The science behind the mask filtering is well-established hence the reason for their use in medical settings. It’s not the size of the virus but the size of the aerosol particles which are huge compared to the virus itself. Also, as Chronos already mentioned, the filtering mechanism of N95, KN95, and even surgical masks rely on electrostatic attractions that are highly effective.
Here’s a simple breakdown on the physics and chemistry behind masks.
While surgical masks would not help you if you were in an enclosed room with a covid patient, even they reduce the chances of catching covid in moderate-risk setting like a grocery store.
Of course, masks work extremely well in protecting others from your germs since they prevent the formation of small aerosols by simply increasing the humidity high behind the mask. Again, this is also firmly established science.
I started a thread a year and a half ago on this which was probably a year after the efficacy of masks against SARS-CoV-2 was pretty firmly resolved.
@Retzbu_Tox provided some great links in this post