noCountryFlags: false does still hide flag emojis on ms windows with the native emoji set.
I replace the native emoji font inside of my css, with google noto color emoji which does support country flags:

@font-face {
  font-family: 'EmojiMart';
  src: local('Apple Color Emoji'), url("noto/emoji/NotoColorEmoji.ttf") format("truetype");
}

But emoji mart checks only for the native font and does not notice that the 'EmojiMart' font was set:

Possible Solutions

A. noCountryFlags property should respect false

noCountryFlags should autodetect when it is set to undefined and respect my preference when I set it to a boolean true or false:

noCountryFlags = undefined // auto detect support
noCountryFlags = false // show country flags
noCountryFlags = true  // hide country flags

PR that implements this solution: #809

B. isEmojiSupported() check should include 'EmojiMart' font

probably easy to do (just add it to native-support.ts#L64), but there is the question whether this introduces a race condition where the css stylesheet is loaded after emoji mart did the check.