Looking at the Python source code Modules\_tkinter.c, TCL uses hard coded location of tcl_library_path to find its initialization files which doesn't work when Python is loaded by MATLAB.
Here is an workaround:
>> setenv('TCL_LIBRARY', 'C:\Users\sji\AppData\Local\Programs\Python\Python38\tcl\tcl8.6')
>> setenv('TK_LIBRARY', 'C:\Users\sji\AppData\Local\Programs\Python\Python38\tcl\tk8.6')
>> py.tkinter.Tk
Run these commands every time you run MATLAB. Alternatively, place the commands in a MATLAB startup script.
