Navigation Block | Select Menu -> Dropdown list Problem

I’ve modified a menu multiple times to get it just right. However, the only way I can consistently see the correct menu in my pages is to choose it by name from “Classic Menus” at the bottom of the “Select Menu” dropdown list. There is a long list of items in the regular “Menu” choices above the classic menus that all have the exact same name. If I select one of them, a previous iteration of the menu is displayed that is no longer defined under Appearance | Menus. The list grows longer every time I modify the menu. Also, every time I update a menu, I have to update each of the pages where it’s used by selecting the latest iteration from the “Classic Menus” options. (There are no duplicate names there.) Shouldn’t the modified menu be updated automatically in every navigation block where it is selected?

I’m using WordPress 6.0.2 with the Gridiculous theme and very few plugins, all of which are up-to-date. PHP is at version 5.6.40. which I’m hesitant to upgrade without knowing any of the site’s history.

Has anyone else seen this problem or know of a solution? I’d appreciate any help.