Hi,
Thanks!
I have looked at the theme files quickly via the theme editor, but there is no searchform.php file. That very likely means, that the search form is very likely hard-coded. It was probably different before the theme update, and the author decided to use a different method. The WordPress and WooCommerce override methods did not change recently, so it must have been a theme related change.
I tried to locate the hard-coded form file within the theme files, but I could not find it there. Can you please ask the theme author where it is located? After that it should be possible to replace via the code editor.
Another possibility is to try the plugin as a menu item, since I see it is already within the navigation menu.