Apple has released the iOS 18.6.1 official update for iPhone users, following up on the previous official release just 16 days ago. This update is specifically tailored for users of the Apple Watch in the United States, reintroducing the blood oxygen monitoring feature for the Apple Watch Series 9, Series 10, and Apple Watch Ultra 2. The measurement results will be processed on the iPhone and presented within the Health app. For iPhone users in Mainland China, this update does not introduce any notable new features.