noto-emoji-ttf not working correctly

emacs28 supports emojis in color (so far they were in
black&white). The documentation I found says it prefers the Noto Color
Emoji font, which is packaged as fonts/noto-color-emoji.

However, with that font installed, when I open the attached example in
a graphical emacs, I get empty replacement boxes.

M-x describe char says:

    ftcrhb:-GOOG-Noto Color Emoji-normal-normal-normal-*-13-*-*-*-m-0-iso10646-1 (#x373)

So it uses the correct font and googling tells me that ftcrhb is the
font backend I should expect nowadays.

When I open the same font ("Noto Color Emoji") in libreoffice and try
to 'Insert' -> 'Special Character' I get empty boxes as well. (The
black&white version "Noto Emoji" looks ok.)

So I suspect something's up with the font.

Is the font broken, or is one of our support libraries too old?

That's on NetBSD 9.99.96/amd64 using X from xsrc with pkgsrc from yesterday.
 Thomas

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