When using fonts with ligatures such as FiraCode while the theme is active, the ligatures do not render! However, in the Editor Settings preview [Settings -> Editor -> Font], they are rendered correctly.
The font dependant font ligatures to be rendered.
Ligatures are not rendered.


You need to activate it in Settings -> Editor -> Color Scheme Font.
Most helpful comment
You need to activate it in Settings -> Editor -> Color Scheme Font.