Hi,
That's a setting of Joomla for all the modules. It's not a setting we added to the modules included in HikaShop.
As per the Joomla documentation on that :
Header Tag. The HTML tag to use for the modules header or title. This can be an h1, h2, h3, h4, h5, h6 or a p tag. Note that you must use a module style (chrome) of html5 or add your custom module styles in <mytemplate>/html/modules.php.
docs.joomla.org/Help4.x:Admin_Modules:_Title
So you're right that this setting should define what tag is used around the title of the module.
But as explained there, that setting is taken into account in the chrome of the module.
And so, if this setting is ignored, it's probably because of the code in the chrome of the modules in your template.
And that's why I recommended checking with your template provider.