It looks like Grok is mixing up steam rooms with Finnish saunas. If you leave your sauna wet all the time at low temperatures (90 to 120 degrees is an incredibly low temperature for any real sauna) then yes you may have problems. But with a real Finnish sauna (not the steam rooms Grok keeps talking about) alternating between wet and dry sessions definitely does kill germs, bacteria, and mold.

That's why, for example, Finns would give birth in saunas because they were such a sterile environment.