This app lets you use an Apple Watch with an Android phone

Merge Watch pairs an Apple Watch with an Android phone after initial iPhone activation. The app installs on both devices and requests Bluetooth, health, notification, and battery permissions. It forwards notifications, enables message replies, offers Spotify controls, syncs health data to Google Fit, and shows ECG and sleep data on the phone. Notifications appear only through the Merge app, and full functionality requires a $6 subscription.