The USA CDC has put out a “scientific brief” about what trials have been done on two subjects:

1. Whether a sick person who wears a mask reduces the virus amount going outward towards others.
2. Whether a well person who wears a particular type of mask breathes in a lesser percentage of particles of virus.

https://www.cdc.gov/coronavirus/2019-ncov/more/masking-science-SARS-cov2.html

I condense these as follows:

A sick person who wears a high quality mask catches 60% of the outgoing viruses when wet droplets get caught.

A well person who wears the best filtering mask available might reduce the amount incoming viruses in droplets of more than 1 micron size by 50%.
{Keep in mind a single Covid-19 virus is 0.125 microns in size, so a bundle of six viruses could pass through a hole 1 micron in diameter}

Earlier post #2841278 has more info on masks,
including
“Why has the big Danish 6,000 person clinical trial results on wearing masks not been made widely known”

It sure seems the Danes found a result that some find embarassing.