I think you misunderstand what's been included in Emacs 27. Emacs 27 includes a new font backend based on the HarfBuzz library. The front end bits still need to be worked on according to Eli Zaretskii in this reddit post

I'm wondering if anyone is working on native support

 

It's already supported in Emacs 27, but someone should code the Lisp part of that: define the character sequences to be ligated, figure out when and how to enable which parts of them, etc.

 

Patches welcome.

I think you misunderstand what's been included in Emacs 27. Emacs 27 includes a new font backend based on the HarfBuzz library. The front end bits still need to be worked on according to Eli Zaretskii in this reddit post

I'm wondering if anyone is working on native support

It's already supported in Emacs 27, but someone should code the Lisp part of that: define the character sequences to be ligated, figure out when and how to enable which parts of them, etc.

Patches welcome.