That's literally the study this thread is talking about. It's great that they did it -- it should have been done in early 2020, all over the world. We should have dozens of other studies just like it.
The fact that we don't is an indication of how hard it's been to pursue any sort of science in this area. Almost nobody funds it, you can't get it published if it doesn't fit the public health narrative, and even if you do, the the news media won't report on it, and it might just get censored on social media.
Make that zero. To their credit, the authors of the Bangladesh mask study released the raw data. "The difference between the two groups was small: only 20 cases out of over 340,000 individuals over a span of 8 weeks." Drawing any conclusions from such small amount of data is deeply unserious.
In a First, Randomized Study Shows That Masks Reduce COVID-19 Infections
A large study co-authored by Yale SOM’s Jason Abaluck and Mushfiq Mobarak tested the effectiveness of a mask-promotion program in Bangladesh in increasing mask use and preventing symptomatic infections. The study found that masks significantly lower symptomatic infections, especially among older people and when surgical masks [instead of cloth] are used.
https://insights.som.yale.edu/insights/in-first-randomized-s...