I'll summarize. This is a meta analysis of dozens of studies and reports on covid-19 spread, and use of masks. I'm sure someone will point out that this is a conservative group; however the articles used in the analysis are from a wide variety of sources, including governmental agencies.
Two key findings are quoted below.
This is significant, and it is not the first time this has been reported. The transmission mechanism this spring and summer was thought to be droplets (larger particles that can be stopped by a mask). With the aerosol spread becoming very clear, a surgical or cloth mask will not stop the flow in or out of the virus. Aerosols is how the flu spreads, and the ineffectiveness of masks against the flu is well documented and indisputable. Thus, the article leads to the following:
The article also provides a meta analysis of negative effects of masks. These include reduced arterial O2, increased inhaled CO2, headaches, mold and bacterial infection related to mask moisture retention, self-contamination from improper wearing/doffing of the masks, and "mask mouth" (chronic tooth decay similar to that from methamphetamine use).
The article also presents some studies presenting positive studies of masks, but points out that they made unrealistic assumptions. Finally it presents practical evidence that mask mandates do not result in decreased covid spread. To this I'll add that while there is a preponderance of practical examples (here and elsewhere like the Rational Ground
article previously mentioned on this site) don't over interpret this since there is no control group.