PWA (essentially it applies to most cases) script for iOS and navigation mode detection

index.html

<script>
  //...
  
  // Detects if device is on iOS
  const isIos = () => {
    const userAgent = window.navigator.userAgent.toLowerCase();
    return /iphone|ipad|ipod/.test( userAgent );
  }
  // Detects if device is in standalone mode
  const isInStandaloneMode = () => ('standalone' in window.navigator) && (window.navigator.standalone);

  // Checks if should display install popup notification:
  if (isIos() && !isInStandaloneMode()) {
    // do something
  }
</script>