There's no proof of anything in any study because studies provide evidence, not proof. There is evidence that masks work in many studies. There is evidence that surgical masks are less effective and that cloth masks are least effective. There is no mask of any sort that stops all viruses. But that's not necessary. The only question is whether the mask being used stops enough droplets to be effective in a particular scenario.
“There is evidence that Masks work in many studies”...AND, there is evidence that Masks DON’T work in many studies. If You recall, back in March Fauchi and the Surgeon General both said that Masks do not prevent the transmission of the Virus. They changes their minds under bureaucratic pressure a month and one half later. The emphasis on closures, Masks and the phony statistics that the media bleeps every day are nothing more than efforts to suppress the economy and hurt Trump.