No need to rely on app-specific configs. You can disable it globally in your fontconfig. For example, this disables ligatures in the Cascadia Code font:

  <match target="font">
    <test name="family" compare="eq" ignore-blanks="true">
      <string>Cascadia Code</string>
    </test>
    <edit name="fontfeatures" mode="append">
      <string>liga off</string>
      <string>dlig off</string>
    </edit>
  </match>

Here is someone disabling ligatures for Noto Sans Mono: https://blahg.josefsipek.net/?p=610