You don’t need searchform.php

Searchform.php is only needed if you are actually making changes to the default search form.

While reviewing themes submitted to, I often notice that authors are including searchform.php without making any changes compared to the default form.

Other authors are using

add_theme_support( 'html5', array( 'comment-list', 'comment-form', 'search-form', 'gallery', 'caption' ) );

But replacing the search form with a non html5 form. This is unneccesary.

The Developer Code reference on 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.