TikTok | WordPress.org

A custom follow button is one way at the moment. AddToAny provides the TikTok icon, so the PHP code is a little different:

function addtoany_add_follow_services( $services ) {
    $services['tiktok'] = array(
        'name'  => 'TikTok',
        'href'  => 'https://www.tiktok.com/@${id}',
        'icon'  => 'tiktok',
        'color' => '2a2a2a',
    );
    return $services;
}
add_filter( 'A2A_FOLLOW_services', 'addtoany_add_follow_services', 10, 1 );

Then the publisher/writer/etc. is able to add a link to their TikTok profile in Appearance > Customize (or Widgets), where they can simply input their TikTok username.