I’m Very Confused

This plugin claims that Twenty Seventeen “has no way to display a sidebar on pages.” If that’s true, I must have drawn the lucky straw. I’m using Twenty Seventeen on a site and since the site was upgraded to WP 5.0 (now 5.1), all pages display a sidebar by default, and there is no way to remove it on a per page basis. I thought there used to be an option when editing a page, something in the page attributes, that allowed you to select the page type with options like ‘full width’, ‘no sidebar’, etc, but that definitely isn’t there now. I have combed the web for an hour and can find nothing about anything to do with my problem. I’m completely confused by this. I know this isn’t really a typical support question for this plugin, trust that I am only making this post out of last ditch desperation.