Only in the way I “experienced” 300+C by jumping through a bonfire. You never reach a true equilibrium in a Sauna that hot, but you can reach an equilibrium in 50C when the humidity is low enough.
Apples and Oranges. Saunas have much lower humidity, and also you are exposed for much shorter duration of time. 100C is the boiling point of water; so if you stay for an extended period, you'll probably die.
Some people who live in 50C temperatures do not have access to AC or a reliable water source.
Saunas (at least the way we enjoy them here in Finland) can be pretty humid, because we throw water on the stones of the stove. But throwing too much water can make it intolerable, and lethal if you don't follow your instinct to leave if it gets too hot.
Normally in a sauna it's not constantly so humid that sweating wouldn't be able to keep your body temperature normal (as long as you stay hydrated). Throwing water on the stove raises the humidity just momentarily and makes you sweat at full capacity, but normally you would wait for some minutes before throwing more water.
If air is humid enough, sweating can't cool the body anymore because sweat won't evaporate, so already 35C is lethal in 100% humidity.
Sauna at my gym ranges around 200 F +/- about 10 degrees, according to the thermometer on the wall, so getting close to 100 C. I sit in it about 20 minutes after a workout. Yes I am sweating buckets by the end. It feels good though.
It’s a lot different though, since you can exit the sauna into air that is substantially colder, you can’t escape the desert heat.