It also literally says "The high risk of bias in the trials, variation in outcome measurement, and relatively low adherence with the interventions during the studies hampers drawing firm conclusions."
It does, and that's true, but that doesn't contradict what OP wrote.
They found only mid-to-low quality evidence supporting the use of masks to prevent ILI. That evidence, for everything but the question of "n95 vs. other", showed an effect size statistically indistinguishable from zero.
You're essentially saying that the error bars on that effect size are big. They are. But they're still centered on zero.
The evidence they had was of such low quality that no solid conclusions could be made from it. What they found in the research may not reflect reality. They are explicit about this and stress the need for better research.
> "There is uncertainty about the effects of face masks. The low to moderate certainty of evidence means our confidence in the effect estimate is limited, and that the true effect may be different from the observed estimate of the effect...There is a need for large, well‐designed RCTs addressing the effectiveness of many of these interventions in multiple settings and populations, as well as the impact of adherence on effectiveness, especially in those most at risk of ARIs."
They admit that they were unclear about it and later were even more explicit.
"Given the limitations in the primary evidence, the review is not able to address the question of whether mask-wearing itself reduces people's risk of contracting or spreading respiratory viruses."
The review is not able to "address the question" let alone conclude anything about the impact of mask wearing. The review is inconclusive.
> The evidence they had was of such low quality that no solid conclusions could be made from it.
OK, fine. If I grant this (I don't, but let's run with it...), it means the following is also true: we mandated something based on such low-quality evidence that no solid conclusions could be made from it.
