Pulse Ox tells me to "keep still" even though I'm not moving and won't give me a reading

Same problem. I also can't get heart rate readings. 

Same here. There is another thread discussing this behavior: https://forums.garmin.com/outdoor-recreation/outdoor-recreation/f/fenix-6-series/171981/fenix-6x-sapphire-largely-not-working-hr-no-pulseox

I thought Pulse Ox was supposed to only work when you are sleeping? Unless you have acclimatisation mode set.

I just bought a 6X Sapphire, am on the latest software versions and am having the "keep still" error on the pulse ox widget. heart rate is working fine though. Are others still having this problem too?

You can force a reading through the widget at anytime.  

I've tried forcing it but it still won't read, just gives me the "keep still" message over and over. the HR looks fine, no crazy spikes. i tried it laying down to keep as still and calm but still nothing. I only managed to get it to read once so far. no idea what's going on.  I like the watch otherwise but this is a bit disappointing

Maybe the watch is not on tight enough?

I tried tightening to the point where it was leaving a mark on my arm it but didn't work either unfortunately.

Here's a photo of the backside of the watch, I saw another thread where people were discussing those small white parts next to the sensors, and if that indicates a defect, did anyone get more info on that?

Thanks for the help with this guys!

Clean skin, no tattoos, clean and dry sensor? I used to have this problem too but it was solved with software upgrades