Searchform.php is only needed if you are actually making changes to the default search form.
While reviewing themes submitted to WordPress.org, I often notice that authors are including searchform.php without making any changes compared to the default form.
Other authors are using:
But replacing the search form with a non HTML5 form. This is unnecessary.
The Developer Code reference on WordPress.org explains how get_search_form() first attempts to locate the searchform.php file in either the child or the parent theme, then load it. If it doesn’t exist, then the default search form will be displayed.