If there wasn’t evidence, they wouldn’t approve it. Just find the vaccines’ homepage and follow the footnotes.
And before I get lynched: I am all for the vaccine since that has been tested to work and I still wear a silly mask even as it does nothing since I'm tired of people complaining.
No idea where you are buying your masks though.
Even my local national health institute says that masks only protect against droplets from coughing, sneezing, or talking when in close proximity. Which I can grant you, but normal people shouldn't be coughing or sneezing into other peoples faces anyway. Which only leaves talking, but I don't see why grocery store is a place to socialize anyway.
IMO masks are only a thing because helpless people had the need to "do something" and masks are visible way of showing you are doing your part. Plus it didn't help that right wing nut jobs started a war against masks.