Permanent brain damage from oxygen deprivation is scientific fact. Oxygen deprivation lead to cerebral hypoxia with well studied effect. There are enough solid scientific papers on that topic. It is absolutely correct to suppose that any level of oxygen deprivation earlier or later could become a cause of brain damage. Human body certainly could compensate oxygen deprivation for some time and to some extent, but there are no any studies of how long exactly that ability works and what will happen if noticeable oxygen deprivation at levels of mask wearing will last for years.

Also, we were told numerous times that oxygen deprivation from COVID-19 is a cause of brain damage in those who had severe case of COVID-19 in hospital and that's why everybody have to take a jab.

You also could easily notice that persons who still obey mask mandates and constantly wear mask in correct way (not on their chin, as most who obliged by employer do) are much dumber than normal people.

IDK about US, but in Russia surgeons obliged to change surgeon mask every 40 minutes or so and have a rest without mask for some time during that change, IIRC. And they get a good money compensation for heavy conditions of work, just like any other worker who had to wear some potentially harmful, or even just uncomfortable PPE.

AFAIK, children in schools where mask mandates inplemented don't have any rest time, punished for wearing mask formally on a chin and didn't get good money compensation for heavy contitions of work.

In any case - do you have any data showing that surgeons IQ is not lowering with time they spend wearing masks? Or may be there any papers with such research or at least publically available data with results of periodic IQ measuring of surgeons along with their legth-of-service we could use to check your theory?

May be wearing that stupid stone-age tissue sugical masks by doctors is a direct cause of one of the reasons why medical error took leading places in top of death causes.