One can compensate with (steam)pressure and/or duration. Or cold brewing.

In practice I note not that much difference at about 2500m altitute, where my main residence is. French/Aeropress suffices. 100°C isn't necessary. Even only 90°C suffices.

Similar for good Tea. You destroy that with 100°C. Very good Tea should be brewed at 60 to 70°C for greens, blacks more like 70 to 85. Though the hardness/pH of the used water is equally important for them. For coffee not so much.

Yes! I like to vacation in the summer at Mammoth Lakes (~8000 ft ~2400m) and coffee is a bit of a problem. I like weak coffee and compensate for altitude by adding more grounds, but it's really not the same.

Espresso machines work at high pressures (8-9 bar) so it's less of an issue with those. I went up to the observatory on Mont Blanc a few years ago and had an espresso there. That's 3500 meter. I definitely was out of breath. The coffee was fine.

Coffee takes compensation, but even ambient pressure extraction can be tuned for great results — Denver and Boulder have good coffee scenes, for example. The bigger challenge is that Mr Coffee style brewers (bubble pump) have no way to adjust extraction time; and some fancier brewers try to closed-loop control temperature, and end up boiling the water continuously while brewing. Pour-overs obviously give you control to succeed, but for traditional machines I’ve found it critical to find one that allows a set point temperature JUST below local boiling, as well as time adjustment. The Breville Precision is my current workhorse, although I have some mixed feelings about it.