A Randomised Controlled Trial of mask-wearing conducted in Denmark (with over 6,000 participants) finds no statistically-significant evidence that masks reduce the risk of COVID infection to the wearer: https://www.acpjournals.org/doi/10.7326/M20-6817

The study does not attempt to quantify any benefit to those other than the wearer; indeed it would be very difficult to design an ethical RCT that did so, because this would require potentially-infected individuals to be instructed not to isolate.

Nonetheless, this study suggests that masks are not effective at blocking COVID virus transmission.

The last tweet above is my own opinion, based on the fact that I cannot see an infection mechanism for which masks might be effective in one direction but not the other.

Then, there is overwhelming statistical evidence that masks are ineffective. France and Spain with masks-everywhere mandates going back months with huge spikes in cases, and Scandinavian countries with no masks and much lower rates.

Finally, "but what about South East Asia"? https://twitter.com/stevebrown2856/status/1323692555452751872?s=20