Paper I saw on homemade masks compared to N95 masks. Said ones made out of tee shirt material were not as good but not useless. The authors also pointed out they also work by preventing the wearer from touching their mouth and nose.

Frankly I see no downside to people wearing homemade masks.

Edit: More friendly article that references the paper I'm talking about.

https://smartairfilters.com/en/blog/best-materials-make-diy-...