The core WordPress Menu widget gives you the list. You can style it to look like a table with two columns. Or you could have a little code that calls the same function that the Menu widget calls, with slightly different parameters, so it is output a little differently.

All I want is a list of the URLs in my main WordPress menu to check which pages are not in the the main menu. I can do this manually, but that would be very tedious. There must be some way to do it automatically.

Thanks!

If you open your site in one window and use another window to view your list of Pages (which is shown in menu order), would that help?
If not, you can use your browser to View Source of your site’s page and see the HTML for the menu. I would think it would be easier to see the actual menu than the HTML for it.

Or you can build a new menu and click the box Add All Pages, then arrange them how you want (and add whatever other things you wanted). Then swap the old menu for the new one.