Gravity Forms use enhanced UI on select drop down for lists

gf-enhanced-ui-list-select.js

<script>
    // For standard forms
    jQuery( document ).on( 'gform_post_render', function( event, form_id, current_page ){
        gformInitChosenFields( '#field_12_10 select', 'No results matched' ); // Change selector to #field_FORMID_FIELDID
    });
    // Forms that use multiple pages and ajax
    jQuery( document ).on( 'gform_page_loaded', function( event, form_id, current_page ){
        gformInitChosenFields( '#field_12_10 select', 'No results matched' ); // Change selector to #field_FORMID_FIELDID
    });
</script>

gf-enhanced-ui-list-select.php

// Add to functions.php - this enqueues the Chosen.js JavaScript library
add_action( 'wp_enqueue_scripts', function() {
  wp_enqueue_script( 'gform_chosen' );
}, 999 );