Viral particles often ride on water droplets (like from a cough), and a mask *can* stop those. Focusing on just the size of the actual virus is not helpful.
Virus size is important as it means even a small droplet can carry enough virus “cells” to infect anyone — unlike bacteria. And, a small droplet that can do this is as small as 2.5um. That is small enough to stay airborne indefinitely and pass thru any mask. Cloth masks pass 97%. Yes, pass.