It was this one... https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7191274/ - a while ago. I don't think the evidence suggests that masks were ever the panacea for the whole Covid outbreak. So even with a mask I didn't go out all that much. I think they're likely to be phased out fairly soon - that certainly seems to be the case here in the UK.

BUT... and it's a big but... wearing masks reduces anxiety in fellow members of society. It doesn't hurt me to wear a mask, it doesn't interfere with my life too much. It's a minor inconvenience at best - and even if there's not a huge level of protection offered, I'd suggest that it'd least protect against other infections like influenza if they arrived at the same time. I think that's more true as we head into winter flu season over the next few weeks.

The 'where required' bit is the important bit for me. I think that 'requirement' shouldn't be mandated by law - but it is incumbent on everyone to take into account the unwritten social contract and attempt goodwill and inclusivity to all people.