Adding icons to widget titles

You can easily add icons to your menu items. Simply add the FontAwsome class between [icon] & [/icon].

Example Code:

[icon]far fa-clock[/icon]

Result:

You can find a list of the icon class names at FontAwesome.

Final step:
Add the following code to your child theme's functions.php file or using a Readymade Plugin like Code Snippets:

// Add Shortcode (font awesome) in widget title and menu items
add_shortcode( 'icon', 'listimia_shortcode_fa' );
if ( ! function_exists( 'listimia_shortcode_fa' ) ) {
 function listimia_shortcode_fa($attr, $content ) {
 return '<i class="'. $content . '"></i>';
 }
}
add_filter( 'widget_title', 'do_shortcode' );
add_filter( 'wp_nav_menu_items', 'do_shortcode' );

That's all.