even holding your breath for couple seconds will tank saturation, so pretty likely high altitude will do the same until your breathing adjusts to compensate
It shouldn’t effect your oxygen saturation’s at all. Respiration is driven by raised CO2 not drops in oxygen in the healthy (COPD is the classic example of where low oxygen levels drive respiratory effort)
I know I replied to a different comment of yours, but this paper also illustrates how this point, while matching common medical wisdom, is not necessarily correct when accounting for altitude: https://www.thelancet.com/journals/langlo/article/PIIS2214-1...
(Summary: Healthy children at higher altitude breathe more rapidly.)