I'll give this crack. I believe the current state of knowledge is that it likely works like this:

Mask on virus spreader: Mask will capture a very large amount of the viral load being shed.

Mask on non-spreader: Will filter some amount of the air you're breathing in and lower your initial viral load. Giving you either

A) a low enough dose your immune system kills it off or

B) a low enough dose your immune system has more time to mount a defense before the viral load in your body rises high, potentially leading to a more mild infection.

That's why we ALL need to wear a mask and stay 6ft/2 meters apart.

BTW, further is better 6ft is not a magic bubble.

Also there is aerosol transmission(floating covid in the air). Ventilation is CRITICAL for this to be stopped. Germany is spearheading ventilation as a way to stop the spread as far as I know.

They are making rules about intervals windows need to be opened etc.

Heres a BBC article covering Germany on this: https://www.bbc.com/news/world-europe-54599593

Here's a random blog that gets into it: https://dirkpaessler.blog/2020/08/13/corona-wie-co2-messgera...