Depends on your definition of mask. If you are talking about an N95 or better that is replaced with a new one every two hours then it can certainly help with droplets. Does not work very well with aerosols which have the highest distance of movement over droplets. Having said that, covering your mouth when you cough or sneeze is about as effective as a mask. But if you are talking about the homemade masks and especially the gators then not so much. People wear them for hours and days on end and the data shows that after two hours they are pretty much useless and likely do more harm than good in spreading disease.
But this study seems to imply they do almost no good and in fact may be harmful to people wanting to avoid infection. If they did nothing you wouldn't expect to see any correlation with rates of infection but in fact we see the opposite. Those that seem to wear them the most are more likely to get the virus. We need to find out if that is true on a broader basis, and if so, why. I suspect it is because the ones wearing a mask engage in much riskier behaviors....but that's just a guess. It is also possible that we wouldn't see as strong a negative correlation with a larger study population. But based on the statistical analysis used by the authors I would be surprised if the results would be dramatically different....but it is possible.
And to repeat myself for probably the 20th time, the problem I have with masks is they give people a false sense of security and they become more relaxed with the other measures that are more effective and actually work. As an analogy...do you ever wonder why rugby has far fewer serious injuries than football? I don't. Rugby players are not wearing all the protective gear that causes football players to engage in very risky behavior. The same is true with masks. I see it all the time and if you were honest you would agree. People with masks do not social distance well and probably are not as diligent with personal hygiene. So wear your mask but stay way from me and don't engage in the behaviors that risk infection if you are over age 65, have co-morbidities or must be in regular and lengthy contact with those that do. Otherwise go about your business and you will be like the vast majority of us that have never been infected. And even if you do, hopefully you will be in the 99.8%+/- that don't succumb to the virus.