Its not really about humidity but the chance water will drop out of the air and become available to mold spores already present.
Many grow in higher humidity just fine, moving air cannot build around bud and allow it to reach saturation point.
You can check the science of humidity for how it really works. Above 70% is not mold but it starts to increase the chances, you might start finding a hot stagnant area more prone at higher humidity.
Theres a lot of fluctuation from high to low at night to day, dry to rain and temperature differences elsewhere but deserts and rainforests can keep steady numbers for much longer than your average temperate or tropical zone.