Masks are effective, something I believe the CDC dropped the ball on at the beginning.
While most aren't fine enough to filter out some virus sized particles, some are.
Surprisingly including some of the finer HVAC filters used mostly in labs.
Even more surprisingly, the non-woven fabric many reusable shopping bags are made from is very nearly equivalent to N-95, sometimes probably better. It's just not certified as a healthcare filter material.
What they do, and should have been obvious is to slow down the exhaled air, giving the particles less push to travel the same distance in the air.
In other filtering situations, it's also well known that any filter is better than none.
A video showing the difference in different situations.
https://www.youtube.com/watch?v=UNCNM7AZPFg
And another explaining how much is stopped by what from a study using actual Covid.
https://www.youtube.com/watch?v=3GndKYJ4uBI
I live in a city with a fairly high asian population, and it wasn't at all unusual to see someone -especially the elderly wearing masks before this, even outside of flue season.