Google now allows iPad and iPhone users to verify sign-ins into Google and Google Cloud services using the security keys built into Android phones running Android 7.0 or later. The Android built-in security key was introduced by Google during Cloud Next 2019 to provide a simple way to prevent phishing attacks which are currently a huge threat both home and business users. Users have to enable Bluetooth on both the Android phone and the device they want to sign-in on, and install the latest version of Smart Lock app.
Source: https://www.bleepingcomputer.com/news/security/android-s-security-key-now-verifies-sign-ins-on-ios-devices/