I recently decided to change my emoji font from noto to twemoji and applied the change by creating the following ~/.config/fontconfig/fonts.conf:
<?xml version='1.0'?>
<!DOCTYPE fontconfig SYSTEM 'fonts.dtd'>
<fontconfig>
<alias>
<family>sans-serif</family>
<prefer>
<family>Noto Sans</family>
<family>Twemoji</family>
<family>DejaVu Sans</family>
</prefer>
</alias>
<alias>
<family>serif</family>
<prefer>
<family>Noto Serif</family>
<family>Twemoji</family>
<family>DejaVu Serif</family>
</prefer>
</alias>
<alias>
<family>monospace</family>
<prefer>
<family>Noto Mono</family>
<family>Twemoji</family>
</prefer>
</alias>
<dir>~/.fonts</dir>
</fontconfig>
It seems to have correctly changed the emoji font in every application with the exception of the emoji selector which is still using the noto emojis. Is this a limitation with the kde emoji selector or is additional configuration needed?