From the help popup of that option:
The title values provided by WordPress may include modifications by themes and/or SEO plugins (appending the site name or expanding inline variables, for example, is a common practice). Uncheck this option to always use the original unmodified title value from WordPress (default is unchecked).
WPSSO does not modify the <title> value – that is not a feature related to meta tags or Schema markup, which is the purpose of the WPSSO plugin. As explained above, WPSSO uses the original unmodified title value (by default) for its meta tags and Schema markup.
If you need to modify the <title> value for your webpages, then WPSSO is not the plugin for this.
See here fore more info on the WP title filter: https://developer.www.ads-software.com/reference/hooks/wp_title/
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