How to SEO optimize articles published on WordPress?

Everything you need to do — check the appropriate box in the “Publish” tab:

And then install (if they have not already been installed) the plugins: Yoast SEO And REST API Meta Support. The first plugin provides SEO optimization, and the second plugin provides setting values in the fields of the first plugin via the API.

If SEO optimization is not working for you - most likely, you either did not check the box above, or did not install any of the above plugins. To date, no further cases have been identified where this problem could occur.