Apple has released watchOS 8.5.6 for the Apple Watch. It enables the ECG app and irregular heart rhythm notifications for wearers of the smartwatch in Mexico. It also includes improvements and bug fixes.
WatchOS 8.6 can be downloaded for free through the dedicated Apple Watch app on the iPhone by going to General > Software Update. To install the new software, the Apple Watch needs to have at least 50% battery, it needs to be placed on a charger, and it needs to be in range of the iPhone.