As for studies that do meet standards, they are hard, not easy, to dismiss. That work tends to get meta-analyzed and synthesized, not brushed off, at least by the reader community at large. I wish more of it got replicated, too, but that's a different thread.
Meanwhile, we still have to make decisions. But not entirely without scientific guidance. We can reason from studies of how the disease spreads and how potential countermeasures work. We can argue by analogy to what science has revealed about apparently similar phenomenon, like flu. Those aren't scientific arguments so much as other kinds of arguments hopefully informed by science. Pending better science as such, that's what we've got.
It seems reasonable to me to think that, whatever the scientific contribution of the study, the fact that it doesn't test the primary claimed benefit of masks suggests that it is not the last word on the matter. When I say 'I would not be quick to promulgate or depend on the study', I am not dismissing the study, but recognizing its limitations, as do the authors.
Once these factors are removed its unlikely that mask wearing provides any value beyond security theatre.
It seems obvious by now that universal mask policies have not been very effective at controlling the transmission rate when compared to other variables: known and unknown. Maybe it is a little bit effective but that has not been conclusively shown yet. Where I live, the Ro value dropped below 1 before masks were required and shot well above 1 months later. Compliance is high, probably as high as any public health policy