If this mask ‘wonder-drug’ were true, then the whole thing would have disappeared in Germany back in late June in Germany...because of massive mask requirements.
I got curious about how Germany performed since you brought up the comparison and I haven't looked at them before. Here's the comparison of daily COVID-19 deaths per 100,000 people:
Source: https://covid19.healthdata.org/germany
Note that the "observed" figures only run through July 7th, so the data is a little over a week old.