This is a great summary of good fonts to try in case you haven’t seen it (although I haven’t found any that don’t have at least one odd ligature issue):
There was also some questions about this on e.g. the Fira repo,
and someone lists pretty detailed instruction how one might go about compiling a custom version of the font with customized ligatures. It would be awesome if someone made a Julia-specific version and could share it!
As a general remark about ligature-heavy fonts for Julia, see this comment from one of the FiraCode authors:
Fira Code is for languages that don’t support Unicode and resort to ASCII pseudo-graphics instead, for historical or other reasons. If you can use full Unicode range, I definitely recommend that (I believe that’s the future) and you probably don’t need something like Fira Code