How to install tkinter for python 3.9 on xubuntu 20.04?

I have just installed python 3.9, but it doesn't come with tkinter apparently. When I try

sudo apt install python3.9-tk

I get the message

Note, selecting 'python3-tk' instead of 'python3.9-tk'
python3-tk is already the newest version (3.8.10-0ubuntu1~20.04).
0 upgraded, 0 newly installed, 0 to remove and 11 not upgraded.

Python 3.8 is the system default. How can I get tkinter for python 3.9?

UPDATES

As suggested by ubfan1, I tried

dpkg-reconfigure python3-tk

but I got the error

FileNotFoundError: [Errno 2] No such file or directory: '/usr/lib/python3.9/tkinter/__init__.py'

I made a tkinter directory and added empty files for each file that dpkg complained about. (Every file in the tkinter directory, so far as I can see.) Then dpkg-reconfigure ran with no errors, so I tried

sudo apt install python3-tk

again, and I got the same message as above, telling me that the newest package was already installed. I was able to import tkinter in python 3.9, by root=tkinter.Tk() failed. On inspection, all the files in /usr/lib/python/ were still empty, so I decided to copy all the scripts from python 3.8. This time, python told me no module named _tkinter. I found a module named

_tkinter.cpython-38-x86_64-linux-gnu.so

in /usr/lib/python3.8/lib-dynload and I copied it into /usr/lib/python3.9/lib-dynload replacing the "38" in the name with "39".

This seems to have worked, in the sense that tkinter runs under python 3.9, but I need hardly say that I don't feel entirely comfortable with this. What's going to happen when I upgrade to python 3.10.?

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