After enabling Yoast SEO plugin, I notice that site title is suffixed to page title in all post individual pages.
Upon searching I find that it is Yoast plugin adding site title with page title.
In order to remove Site title, go to SEO -> Search Appearance -> Content Types.
In Content Type tab, under Post section, you will be able to see SEO Title input. There keep Title and Page. Remove Site title and Separator. Then save your changes.
You individual page, title would be without site title now.