How to save the Additional CSS in a CSS file and enqueue it

add_action('customize_register', 'theme_footer_customizer');
function theme_footer_customizer($wp_customize){

// Get upload directory
    $upload_dir = wp_get_upload_dir();

    // Create style file path
    $style_file_path = sprintf( '%1$s/css', untrailingslashit( $upload_dir['basedir'] ) );

    // Create directories if they do not exist
    if( ! file_exists( $style_file_path ) ) {
        wp_mkdir_p( $style_file_path );
    }

    // Sanitize contents ( probably needs to be sanitized better, maybe with a CSS specific library )
    $contents = wp_filter_nohtml_kses( wp_strip_all_tags( wp_get_custom_css() ) );

    // Replace the contents of the file with the new saved contents.
    $style_file = $style_file_path . '/my.css';
    file_put_contents( $style_file, $contents );

}
remove_action( 'wp_head', 'wp_custom_css_cb', 101 );
// /* How to Enqueues the external CSS file */
add_action( 'wp_enqueue_scripts', 'my_external_styles' );
function my_external_styles() {
    $upload_dir = wp_get_upload_dir();
    wp_register_style( 'my-css', sprintf( '%1$s/css', untrailingslashit( $upload_dir['baseurl'] ) )  .'/my.css' );
    wp_enqueue_style( 'my-css' );
}