… a agregar un botón de compartir

Amiguito SHARE para meter como link y que en dispositivo lance las opciones de compartir.

if(navigator.share !== undefined) {
    document.addEventListener('DOMContentLoaded', e => {
      var shareBtn = document.querySelector('div.share a');
      shareBtn.addEventListener('click', clickEvent => {
        clickEvent.preventDefault();
        navigator.share({title: document.title, text: window.location.href, url: window.location.href})
          .then(() => console.log('Successful share'),
           error => console.log('Error sharing:', error));
      });
    });
}

Esta joyita la encontré en https://paul.kinlan.me/navigator.share. ¡Gracias!

Le hice una modificación para tratar de incorporarlo en el plugin Storefront Product Share combinando algo de PHP y agregando:

		<div class="storefront-product-sharing">
			<ul>
				<li class="twitter"><a href="<?php echo esc_url( $twitter_url ); ?>" target="_blank" rel="noopener noreferrer"><?php _e( 'Share on Twitter', 'storefront-product-sharing' ); ?></a></li>
				<li class="facebook"><a href="<?php echo esc_url( $facebook_url ); ?>" target="_blank" rel="noopener noreferrer"><?php _e( 'Share on Facebook', 'storefront-product-sharing' ); ?></a></li>
				<li class="pinterest"><a href="<?php echo esc_url( $pinterest_url ); ?>" target="_blank" rel="noopener noreferrer"><?php _e( 'Pin this product', 'storefront-product-sharing' ); ?></a></li>
				<li class="email"><a href="<?php echo esc_url( $email_url ); ?>"><?php _e( 'Share via Email', 'storefront-product-sharing' ); ?></a></li>
        <li class="share-redes"><a href="#"><i class="fas fa-share-alt-square"></i> Compartir</a></li>
			</ul>
		</div>
    <script>
      if(navigator.share !== undefined) {
        document.addEventListener('DOMContentLoaded', e => {
          var shareBtn = document.querySelector('.share-redes a');
          shareBtn.addEventListener('click', clickEvent => {
            clickEvent.preventDefault();
            navigator.share({
              title: '<?php echo $product_title; ?>', 
              text: '<?php echo $product_url; ?>', 
              url: '<?php echo $product_url; ?>'
            })
            .then(() => console.log('Successful share'),
            error => console.log('Error sharing:', error));
          });
        });
      } else {
        console.log('Share API no soportado');
        var shareBtn  = document.querySelector('.share-redes');
        shareBtn.textContent = '';
      }
    </script>