happy new year!
i had the same problem in imessage. every time i wanted to get emoji and pressed the smily, the bar turned black. what i did is try to set the decimal separator to . to have emoji work as described by our spanish friend. but it didn't work for me. so i reverted to german decimal separator, which is a ,
closing the imessage app did the trick. before that i tried with the textedit app and emoji were working too.
all in all, not clear what the problem is and what the solution to the problem really is.
<- just added the emoji through the touch bar.