Oximeter / oxygen saturation

Hi


I'm trying to understand the pulse oximeter in garmin 6s pro.

Have you also noticed that it is very difficult for the measurement to take place, there is often the inscription: do not move. Although the hand is motionless.
Any tips / advice?

Why can't we add oxygen saturation monitoring during activity? Or I can't find it.

I thought this would be the added value of this device.