Just to add some more clarification, on your site I can see you are using the Yoast SEO plugin. This plugin does things slightly differently in regards to the static homepage.
When Yoast SEO is active, it will render the header title of the static homepage using the same format of the other pages e.g. “Page Name – Name of site”.
It is not the theme that is doing this, it is the Yoast SEO plugin. It is overriding the standard WordPress way of generating the header title for the static homepage.
To change this, in your dashboard go to the page editor for the page that is set as your homepage and edit the Yoast SEO setting for ‘Snippet Preview’ > ‘SEO Title’.
If you look at the Yoast SEO ‘Search Appearance’ page (Dashboard > SEO > Search Appearance) it explains this like so:
Homepage & Front page
You can determine the title and description for the front page by editing the front page itself.