Been following this thread. I do not remember reading about anyone suggesting the
FAA PROTE (Reduced Oxygen Training Enclosure) [I do not know what the 'P' stands for.]
Before COVID, the FAA had their mobile chamber traveling around the country and one could sign up for it when it was in the area. I was living in PA when they were at KAGC and able to take advantage. I took part in the FREE FAA training.
People are different and one can have different response when deprived of O2. I learned that my hands start shaking when I am deprived of O2. Your response may be different. I do not scuba dive but I understand that they do something similar with divers when they train to dive to different depths.
Back in 2002, I also took an FAA Physiological Training Course at Oshkosh AirVenture 2002 and have a little blue card that says I completed the "Academics Only" part of the Physiological Training.
When I lived out west, I would tend to operate above 9,500 MSL a lot. I carried oxygen (IF I did not have smoke oil on board) and would tend to use O2 above 9,500 if I was going to be flying more than one leg. The use of O2 made flying all day much less fatiguing at the end of the day.
Now that I live back east, I find it rare for me to get the airplane above 7,500 MSL. My O2 tank is 3/4 full. At the present time, I would need a hydrostatic test of my O2 tank to get it refilled.