Install the Noto emoji font and make this file exist:

~/.config/fontconfig/conf.d/999-emoji.conf

999-emoji.conf

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE fontconfig SYSTEM "fonts.dtd">
<fontconfig>
  <match>
    <test name="family"><string>sans-serif</string></test>
    <edit name="family" mode="append" binding="strong">
      <string>Bitstream Vera Serif</string>
      <string>Noto Color Emoji</string>
    </edit>
  </match>
 
  <!-- Add emoji generic family -->
  <alias binding="strong">
    <family>emoji</family>
    <default><family>Noto Color Emoji</family></default>
  </alias>
 
  <!-- Aliases for the other emoji fonts -->
  <alias binding="strong">
    <family>Apple Color Emoji</family>
    <prefer><family>Noto Color Emoji</family></prefer>
  </alias>
  <alias binding="strong">
    <family>Segoe UI Emoji</family>
    <prefer><family>Noto Color Emoji</family></prefer>
  </alias>
  <alias binding="strong">
    <family>Emoji One</family>
    <prefer><family>Noto Color Emoji</family></prefer>
  </alias>
</fontconfig>