Ubuntu – Only Squares Displayed Instead of Letters and Numbers in Ubuntu 18.04

Having fonts-noto-color-emoji was not enough also for my Ubuntu 18.04 system.

However, there is another answer to the question you linked to: https://askubuntu.com/a/1029675/188679

Create a file ~/.config/fontconfig/conf.d/01-emoji.conf and put the following content inside:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE fontconfig SYSTEM "fonts.dtd">
<fontconfig>
  <alias>
    <family>serif</family>
    <prefer>
      <family>Noto Color Emoji</family>
    </prefer>
  </alias>
  <alias>
    <family>sans-serif</family>
    <prefer>
      <family>Noto Color Emoji</family>
    </prefer>
  </alias>
  <alias>
    <family>monospace</family>
    <prefer>
      <family>Noto Color Emoji</family>
    </prefer>
  </alias>
</fontconfig>

Then, run fc-cache -f -v. Finally, restart Chrome.

There is something common about the applications you mentioned, viz. Calculator, Characters, System Monitor and System Logs, they are all pre-installed as snap applications instead of in the traditional way (from .deb packages via dpkg/apt). Snap packages are deployed by a package management system called 'snappy' built by Canonical Ltd.

Since you are having this trouble with these specific applications and the fact that the following fixes the issue

I usually delete them and install the same app but with a higher rating (stars) in the software centre.

("the same app but with a higher rating (stars)" is the almost always, if not always, the traditional counterpart of a snap application in the Software centre, snap applications tend to show various issues due to the way they're deployed and their restrictive security features), it is most likely an issue with snaps on your system. Since there is no technical detail provided, it's hard to say what exactly the problem is. It can be any of various possible reasons, e.g. snapd is not installed or corrupted, your PATH is not set up properly for snaps etc.