Hello @scorbelli,
Hope you are doing good.
You can achieve this by minor changing the code. Go to themes->magzimum->search.php file and make the following change.
Replace
<?php get_template_part( 'content', 'none' ); ?>
By
<?php get_template_part( 'template-parts/content', 'none' ); ?>
This should do the trick to show “Nothing found” when the search couldn’t find any result.
Hope this will help resolve your issue.
Regards!!