If you wish to disable all calls to the Google Fonts API, simply integrate the following snippet. It completely removes all calls to the API, though third party plugins might still fetch Google Fonts.

add_filter('blocksy:typography:google:use-remote', function () {
  return false;
});

add_filter('blocksy_typography_font_sources', function ($sources) {
  unset($sources['google']);
  return $sources;
});