blood oxygen app

I know that if you have the Watch too tight or too loose that you can get a reading like that. Here is a support document with troubleshooting steps. See if this helps you. How to use the Blood Oxygen app on Apple Watch Series 6 - Apple Support Make sure you are following the steps for measurement, being still, letting your arm rest on a table or your lap, etc.

What happens when you tap Start after opening the Blood Oxygen app? You should see a 15 second timer after tapping on Start, and you have to wait for that to complete. Can you describe what is happening and what you are seeing. Also, what series of Watch do you have, what version of watchOS you have and what version of iPhone the Watch is paired to. Also, where are you located (country).

At this point, I would recommend that you contact Apple Support. Mine seems to work just fine. I'm getting regular measurements during the day, and I can create one at any time. There could be something wrong with your Watch, but only Apple could diagnose that.

Are you in a country that supports the app?;

watchOS - Feature Availability - Apple