Elementor custom fonts in font control

functions.php

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