Hi,
I'm trying to add out of box LETTER entity to timeline add option, so that I can create new letter record from timeline. Although I enabled Quick Create and the Letter entity is already enabled for unified interface.

But the letter entity still does not show up under Add (+) button of Timeline control. When I created another entity "Custom Letter" of activity type, it does show up:

Is there a way to add LETTER under Add (+) button for creation?
Thanks,