Displaying emojis/symbols in Python using tkinter lib
There's a bug in Tkinter that it doesn't transparently map this for you, and definitely a bug in the underlying libraries (Tcl and Tk) that the string is not accepted as is and needs intervention at all. The state is that the underlying libraries currently require that the non-BMP characters in strings be encoded as surrogate pairs.
A little searching here provides code for actually doing this encoding.