MacOS: New Mongolian Cyrillic Keyboard

MacOS 10.15 Catalina includes a new Mongolian Cyrillic keyboard, but it does not do the Command level correctly, so that common shortcuts for copy/paste, etc. do not work.  A custom keyboard which fixes this problem can be found here.

MacOS: Customizing the Accent Popup Menus

For a good and up-to-date instruction on how to customize the press and hold popup menus in MacOS, see this page.