Thanks for opening a support topic @a4jpcom. This opportunity you’re seeing is a PageSpeed Insights metric, and not something that is impacted by using Site Kit. It’s also not something that can be addressed within Site Kit, as in order to address this it requires changes to all links on your website. Modifying your site content isn’t something within the scope of Site Kit, although PageSpeed Insights can help you flag where such opportunities occur as you discovered.
You’ll find out more on this opportunity specifically, and how to address it by visiting this resource.
You can also use the Search Console Help Community for more assistance on this opportunity you’re finding within PageSpeed Insights.