Add theme fonts to Elementor' Style Font Family Select Menus

elementor-custom-fonts.php

<?php
/**
 * Elementor Custom Fonts
 * Source: https://merianos.wordpress.com/2017/09/22/elementor-register-custom-font-family-in-the-fonts-control/
 */

function modify_controls( $controls_registry ) {
	// First we get the fonts setting of the font control
	$fonts = $controls_registry->get_control( 'font' )->get_settings( 'options' );
	// Then we append the custom font family in the list of the fonts we retrieved in the previous step
	$new_fonts = array_merge( 
		[ 'Font Name 01' => 'custom' ], 
		[ 'Font Name 02' => 'custom' ], 
		[ 'Font Name 03' => 'custom' ], 
		$fonts );
	// Then we set a new list of fonts as the fonts setting of the font control
	$controls_registry->get_control( 'font' )->set_settings( 'options', $new_fonts );
}
add_action( 'elementor/controls/controls_registered', 'modify_controls', 10, 1 );