Don't think i've read anywhere, ever, that the mask will stop COVID spreading.
I think what has been mentioned, is that COVID spreads majority through droplets, which, if wearing a mask, will absorb some of those droplets, not all, reducing the ability to spread COVID but not stopping it.
I mean, it might all be nonsensical. But as i said before, if it reduces the chances of spreading COVID by even 1%, is that not worth it given we have 45K recorded deaths (65k if you use excess death statistic)?
It might not save anyone though, in which case, you've had to wear a mask for 30 mins whilst shopping in Tesco. Hardly been asked to walkthrough the Sahara barefoot now is it?