Focus keywords do not add any additional data to your page. The focus keyword feature is only an analysis of your page to optimize the keyword usage and density in the page’s content and other metadata (title, meta description, slug, etc).
?
?There is another type of keywords called meta keywords which do add metadata to your page’s source code, however meta keywords have been removed from Yoast SEO Premium as of version 6.3. As meta keywords have not been used by search engines for a long time we have chosen to no longer include them as a feature. We have an article which explains in further detail why we didn’t recommend using them, and why they were disabled by default at the following link: https://yoast.com/meta-keywords/
?
?If you wish to optimize your page for a keyword we would recommend using the focus keyword feature of the Yoast SEO Premium plugin and ?you can read more on the difference between meta keywords and focus keywords here: https://kb.yoast.com/kb/the-difference-between-focus-keywords-and-meta-keywords/