Obviously, the material a mask is made from stops medium sized particles from flowing through some highish percentage of the time. No good faith actor is disputing that. Studies don't control for real world usage, actual public adoption, actual masks, etc. They also do not control for changes in behavior that we'd expect to occur contemporaneously to the time periods mask mandates are adopted (ie, during spikes in infection). When infections go up, I personally stop going places where lots of people congregate - a huge percentage of people change their behavior in ways that are both germane and impossible to track in response to perceived risk. They also do not or can not control for the differences in behavior in the societies that can actually adopt and enforce mask mandates in the first place; ie, a city that refuses a mandate in the face of a spike has citizens that are more risk tolerate (or something) as compared to eg SF.
All conducted in the heat of the moment where saying anything that gives the slightest wiff of "masks don't work" gets you shunned, your career destroyed, and all social media platforms labeling your content as "misinformation".
Yeah... I'm sure all these studies done post-2019 are totally legit though.
But do they show how much mask mandates work in the real world, do they explain why Edinburgh and Glasgow are indistingishable from Mancehster and Birmingham in numbers of cases detected?
Via what mechanism? Were people not wearing masks in Scotland despite the mandate? Were they wearing masks in England despite no mandate? Is there enough difference in behaviour between Glasgow and Manchester to explain the difference?