Allow ICO Files Upload

function custom_allow_ico_upload($mimes) {

    $allowed_mime_types = array(

        'ico' => 'image/x-icon'

    );

    // Merge the allowed MIME types with the existing list

    $mimes = array_merge($mimes, $allowed_mime_types);

    return $mimes;

}

add_filter('upload_mimes', 'custom_allow_ico_upload');

function custom_handle_ico_upload_errors($file, $uploaded_file) {

    if (!empty($file['type']) && $file['type'] === 'image/x-icon' && !empty($uploaded_file['tmp_name'])) {

        // Check the file contents to ensure it's a valid ICO file

        if (mime_content_type($uploaded_file['tmp_name']) !== 'image/x-icon') {

            $file['error'] = __('Invalid ICO file.', 'text-domain');

        }

    }

    return $file;

}

add_filter('wp_handle_upload_prefilter', 'custom_handle_ico_upload_errors', 10, 2);