My steps. On the https://en.wikipedia.org/wiki/Special:GlobalPreferences#mw-prefsection-editing un-checked the checkbox in the leftmost column, push save button. Then I can use "Enable the visual editor" (it was unavailable) on page https://en.wikipedia.org/wiki/Special:Preferences#mw-prefsection-editing . By default it is un-checked so I checked and now "Visual editing" works. Thanks.
Perhaps this behavior should be changed to be more user-friendly? My idea. When "Enable the visual editor" checkbox is unavailable the system should add Note "to make available change your global setting with name "Enable the visual editor" on the page <URL>"