This is what I found (crossposted: https://forums.linuxmint.com/viewtopic.php?f=47&t=219654):
In Rosa (LM 17.3), after installing the fonts-noto pkg, "Noto Sans CJK TC" becomes the first font to match "monospace" -- command:
fc-match -s 'Monospace'
This is apparently caused by the following block in /etc/fonts/conf.d/90-fonts-noto-cjk.conf (a symlink to /usr/share/fontconfig/conf.avail/90-fonts-noto-cjk.conf):
<match target="pattern"> <test qual="any" name="family"> <string>monospace</string> </test> <edit name="family" mode="prepend" binding="strong"> <string>Noto Sans CJK TC</string> <string>Noto Sans CJK SC</string> <string>Noto Sans CJK JP</string> <string>Noto Sans CJK KR</string> </edit> </match>
I copied this file to /etc/fonts/conf.avail and commented out the block in question. Then, changing the corresponding symlink in /etc/fonts/conf.d to point to this new file removed "Noto Sans CJK TC" from the top of the list of fonts matching 'monospace' and the system's default monospace font reverted to what it was before I installed fonts-noto.