I have used Fontforge to remove all ligatures from a programming font; e.g. my monospace font of choice is a aggressively subsetted variant of Fira Code with no ligatures whatsoever.
https://github.com/samboy/CaulixtlaFonts/tree/main/MiscFonts...
https://github.com/samboy/CaulixtlaFonts/tree/main/MiscFonts...
For example, ligatures in Fira Code cannot be disabled when using the Cygwin terminal in Windows (mintty). In that application, for example, “===” looks like three continuous long lines atop each other in Fira Code, with no way to make it look like three equal signs again.
From https://github.com/tonsky/FiraCode
“Fira Code is not only about ligatures. Some fine-tuning is done for punctuation and frequent letter pairs.” Note that without ligature support, a lot of that fine tuning is lost.