LOL! This is the dumbest shite I've ever heard.
I've worked as a health care professional for many years, and I have numerous extended family members who are health care professionals, many of whom work in sterile environments that require masks and/or respirators for up to 10 hours a day. There is absolutely zero evidence that suggests wearing a mask lowers blood O2. The dude in the here even prefaces his horseshit video by stating that he is not educated in health care.
Sulfer refinery workers and phosphorus tappers work 12 hour shifts using respirators that are highly restrictive, and have to undergo annual spirometry (lung capacity and blockage) tests. I had to work with one for years, and I can row 6k (3.73 miles) in 20 minutes without breathing heavy, and I'm a soggy dad-bod.
You guys need to take a look into elevation mask training. Elevation masks are designed to restrict O2 to a certain level, so that athletes at sea level can train for competition at higher altitudes where the air is thinner. I've worn one, and they are not to be taken lightly. You literally feel like you're suffocating if you put one on at sea level that is designed to mimic 3000ft, which is really nothing compared to say, Denver, Colorado at 5800ft. The kind of face masks that are being recommended don't even get in sniffing distance of these devices. I don't recall anyone dying of suffocation by wearing their t-shirt over their mouth. This is literally the same thing.
There are no statistics of people dying wearing elevation masks either. You want to know why? Because we are extremely adaptable to changes in our environment.
You know what we aren't as resilient to? Pathogens.
Look at the number of people who die by strange pathogens vs those who die due to a lack of oxygen from wearing a mask, climbing Mount Everest, and skydiving in total in a given year.
I know what I'm saying doesn't fit your narrative, so please, go on and keep refuting the science. But I challenge you to do exactly what you're preaching: question what it is you're watching and hearing, even if it fits your narrative. Do some real research and verify through peer reviewed science anything that matches or refutes your claims. Or just put on your tinfoil hat and keep jerking each other off over your "secret truth". IDGAF.