I take my kid (Who has a respiratory condition) to hospital at 90.

In my experience if you are in hospital with oxygen because of a respiratory illness, the oxygen would probably be given once you dip below 92-93 assuming they know you have a respiratory condition. Not because that’s the danger level but because they want to be able to tweak the O2 if you fall even lower. Doctors then usually instruct nurses to adjust the flow so saturation stays in the 90-95 range.

People at high altitude or in airplane cabins can be at 70% for hours without even noticing. Meanwhile someone having a dip from 90 to 80 with pneumonia might be gasping for air.