Where is your evidence. Here is mine. From the Royal Society:
As expected, the different estimates show some variation. Still, all suggest that the effect of introducing face mask regulation reduces the reproduction number by 15–40%, a rather big reduction for one single preventive measure. Even at the lower end of this interval (EFM = 15%), a community not using face masks and currently having RNo ≈ 1.2 (with a doubling time of daily cases being less than a month) would change its reproduction number to RFM ≈ 1 if face masks were made mandatory, hence more or less stopping the growth. If instead EFM = 25% the new reproduction would be RFM ≈ 0.9 and transmission would start declining in the community.