Be careful. Some of these links are "globalresearch" web.
It's high "CONSPIRACY-PSEUDOSCIENCE" web.
Check here:
https://mediabiasfactcheck.com/global-research/
The science recommend massive usage of facemask. Does not reduce O2. Virus does not stand by itself in the air, it is inside flügge particles. Facemask are not perfect, but all reduce viral load, if you get infected using facemask, it's more likely you have fewer symptoms.
Check these info if you need:
https://www.ed.ac.uk/covid-19-response/latest-news/masks-block-spread-of-covid-linked-droplets
https://www.ox.ac.uk/news/2020-07-08-oxford-covid-19-study-face-masks-and-coverings-work-act-now
https://www.ucsf.edu/news/2020/06/417906/still-confused-about-masks-heres-science-behind-how-face-masks-prevent
https://www.nature.com/articles/d41586-020-02801-8
Downvote all anti-mask spreaders please.