Another point of reference, 10,000 feet is the limit in aircraft. If pressurization is lost above that altitude, oxygen masks will drop and the pilots will make a quick dive to below 10,000 feet.

OTOH, La Paz, the/one capital of Bolivia, is at 11,942 feet.

https://the18.com/en/soccer-news/most-intimidating-soccer-st...

That tells you a lot about what can happen with slow adaptation / getting used to it as opposed to catastrophic fast change of the environment.

It's kinda true for climate change as well - just over much longer stretches of time.

The local native population does have genetic mutations adapting them to the altitude, as do of course Tibetans.

I've even heard anecdotes that they feel uncomfortable at sea level.

I'm pretty good up to around 10,000 feet these days due to where I live, but I felt like it took a few years.