concatenation of HTML from return functions

My controller is looking something like this.

Each of the methods called generate some HTML. The concatenated HTML variable gives the final render of the page

Is there a better way to generate my HTML to render coming from different functions:

 $html = $renderer->render($clear_form);
 $html .= $this->render_preview();
 $config = \Drupal::config('amu_import_ldap.settings');
 if (null != $config) {
   $submits = $config->get('import_submits');
   $html .= $this->render_ldap_imports($submits);
 }
 $build = [
  '#markup' => Markup::create("
            {$html}
        "),
];
return $build;