Samsung Electronics GmbH
Hello,
Please note that proprietary Samsung Galaxy functions may not be supported by other smartphones. In general, however, the Galaxy Watch3 is compatible with smartphones with Android 5.0 and at least 1.5 GB RAM as well as with the iPhone 5 or newer models with iOS 9.0 or higher. Use the Samsung Galaxy Wearable App (Android) / Samsung Galaxy Watch App (iOS) to connect the Galaxy Watch to your smartphone. Have a look to see if you can find and install the app in the store.
Best regards from Eschborn
Your Samsung Service Team

Have only tested it with Android

In my opinion, the Watch 3 can be used as a watch, but many vital signs cannot be read or analysed with iOS