5. China’s lockdown was effective, what are you talking about?
To your last point, Brazil is a good example of a complete failure of individual level solutions.
The proposed mechanism is that during exhalation (or more importantly speaking and coughing) there are relatively large droplets of saliva/mucus containing viral particles, and these droplets can be catched by masks (they are big and move more balistically, so masks need not be airtight).
But once these droplets are in air, they dry to (much smaller) aerosol that cannot be catched by masks, you would need properly fitted FFP2/3 respirator.
There's lots of debate about whether that's really how respiratory viruses spread, but more importantly, we know it can't be that simple because we can see the effect mask mandates had on case curves (there wasn't any). So however they're theorized to work, real world data disagrees. There can be lots of reasons for this that aren't even related to mask material, e.g. most transmission occurs in homes, care homes and hospitals, all places where you'd expect most transmission to take place because people have to be confined in a small space with other sick people for long periods, and also places where you can't make people wear masks all the time.