As discussed in https://www.phpbb.com/community/viewtopic.php?f=661&t=2582291.

Windows 10 users using the emoji keyboard to select "red heart" are getting Unicode character 0x2764.  Which is correct, but because the Unicode spec says "treat this character as text rather than a picture", text-formatter correctly follows the spec and let's the browser/OS platform display this character instead of using Twemoji.

Given how common a heart emoji is among those who use emojis, it would be helpful to these users if somewhere in the phpBB-specific initialization of text-formatter we added Joshy's suggested additional alias:

$configurator->Emoji->aliases["\u{2764}"] = "\u{2764}\u{FE0F}";

Such that now the character is one text-formatter will want to Twemoji and give a consistent result across platforms.  Including the case of Windows 10 users no longer getting "a black heart" in response to Windows 10 emoji entry.

This isn't anyone's "bug".  Just helpful.