I'm still looking for the answer.
Different meanings of "courses" has confused things, so I'll restate the problem with illustrations.
Here's the Home view of a site of mine, in the Boost theme, on Moodle 3.6.4.
Note that, in the navigation tray, there is no button called "Courses," as there used to be.
If I click on any course, the bread crumbs show "courses" as one of the links. Look for it here:
If I click on "Courses" in the bread crumbs, I get the view I am looking for. It displays course categories and enables me to expand and hide category contents, thus organizing large numbers of courses more easily.
The URL is: https://[moodle-url]/course.
This is a useful view. Obviously, I can get to it by typing the above URL, but there used to be a button, as shown below.
Here is a screenshot of a theme that presents the Courses button in the navigation panel. It is Essential theme, running on Moodle 3.5.4.
Clicking on the "Courses" button highlighted above goes to https//[moodle-url]/courses.
This "Courses" link does not appear under Site Administration/Courses options.
Unless I am missing something, this "Courses" link sees to have disappeared from the commands, though it has remained functionally present.
Does that make my question understandable?
Thanks for your time and attention.