Blood Oxygen not working on Apple Watch Series 10

Where and when did you buy your Apple Watch 10?

...

The removal of the Blood Oxygen feature is the result of an intellectual property ruling from the United States International Trade Commission, which Apple is appealing.

The Blood Oxygen feature is no longer available on units sold by Apple in the United States on or after January 18, 2024. These are indicated with part numbers ending in LW/A.

Learn how to identify your Apple Watch.

...

copied from: About Blood Oxygen availability - Apple Support

An Apple Watch purchased in the U.S. is legally blocked from using the oxygen sensor. This block is enforced even if the Apple leaves the country.

You can let Apple know directly about that by using the Feedback link:

Feedback - Apple Watch - Apple

Apple does not follow these user to user discussions.