The studies that show that masks reduce the R0 of COVID-19 are many and broad. https://www.livescience.com/face-masks-eye-protection-covid-... The latest ones that I have read indicate an 85% reduction of transmission and infection between two people wearing masks, a double 85% reduction.
Where is an instance of a study that indicates the opposite? Absence of evidence is not evidence of absence.
I find it interesting that the paper suggests that contracting COVID through your eyes is twice as prevalent compared to breathing it in. See 3% rate for non-mask vs 6% for non-eye-protection. Why are we not all wearing eye protection too?
> the authors note that the findings on face masks and eye protection are based on limited evidence
You also have to consider second-order effects like a sense of invulnerability from the mask and added social interactions because people feel safer. Those haven't been studied.
Where is an instance of a study that indicates the opposite? Absence of evidence is not evidence of absence.