Did you ever fully acclimate? After 3 years at 6000 ft I still had lower blood oxygen than at sea level. (per apple watch, so take that with a grain of salt)
I can only speak anecdotally about my experience when I was young and now that I am much older. When I was young I went from about 69' MSL to about 6780' MSL when doing a job at the Air Force Academy and we dared each other to run up some stairs. We made it about half way up and fell over laughing and gasping for air. Our team chief that smoked about a half a carton of cigarettes a day walked right past us shaking his head. For about a week or so I had some pressure in my leg near the hip but it cleared up.
I am much older now and a couple years ago I retired/moved from about 600' MSL to 6300' MSL and it took about a half of a year for my body to adjust including some pain in my legs with some associated popping and other weird pressure like feeling similar to what I had when younger but it took longer to go away. Probably too many decades behind a computer and not enough walking. I've had no feelings of self defenestration.
Isn’t Apple Watch and other blood oxygenation just measuring saturation (a relative measure)?
Among other things, Acclimatization involves producing more blood-oxygen carrying capacity (or less if you go back to sea level), which is an absolute measure, not a relative one that the oximeters would pick up.
I've been here 4+ years now, and other than being 4 years older and just coming out of a sedentary 3 year period, I notice zero effects of living (and running, cycling, swimming, hiking) at altitude. Can't say any more than that really.
