The last few updates to kb_text_shape (&kbts) made the library ~10% faster, added support for more variable fonts, and made font parsing much more robust (though not watertight by any means), alongside various bugfixes:
https://github.com/JimmyLefevre/kb

kb_text_shape 2.28 is out and includes support for variable fonts among many other fixes!
https://github.com/JimmyLefevre/kb
https://code.newroadoldway.com/home
&kbts