Isn’t Apple Watch and other blood oxygenation just measuring saturation (a relative measure)? Among other things, Acclimatization involves producing more blood

Isn’t Apple Watch and other blood oxygenation just measuring saturation (a relative measure)? Among other things, Acclimatization involves producing more blood-oxygen carrying capacity (or less if you go back to sea level), which is an absolute measure, not a relative one that the oximeters would pick up.