Missing screen options dashboard

I would guess that a plugin you are using is responsible for this. You could try deactivating all of them – is the option then visible again?

Here in the article, options for hiding are mentioned. Maybe you can check that for yourself: https://www.wpbeginner.com/wp-tutorials/how-to-disable-the-screen-options-button-in-wordpress/

Thanks very much for the encouragement, I had resisted deactivating all the plugins, but went ahead and discovered it was Siteground Central plugin that took over the dashboard with no notification, no settings, no way of knowing. It is a plugin only available to Siteground hosted sites. If it had a reviews page, it would be getting 1 star.