What is the actual up-to-date version of Tkinter? Where do I find information on Tkinter versions?
The latest tkinter version is by definition in the main branch and the latest release therefrom.
The official, python.org distributions of 3.x for Windows and macOS usually have the latest tcl/tk release at the time of 3.x.0.
Tkinter is part of the standard library and you aren’t really meant to be able to upgrade it independently of Python. It doesn’t, as far as I’m aware (or at least can think of at the moment), have its own version numbers. As @tjreedy alluded to, Tkinter depends on Tcl/Tk, which is not Python code and is a separate package that has to be separately installed and has its own versioning. However, the Python installer normally takes care of that for you. If you were actually interested in this version number, normally you can check that from within Tkinter.
Some distributions of Python have disabled or removed Tkinter for various reasons (especially if it came with your system). If you install a fresh Python from python.org it should definitely include Tkinter. If for some reason you need or want to add Tkinter to some Python distribution that’s missing it, you may find useful information here:
Disclosure: I wrote this up, and I initially joined here primarily as part of doing research for it.
I would just like to reiterate up front: do not attempt to use Pip to install Tkinter. In most cases, to add Tkinter to a Python that came with your system, you should use the package manager that came with your operating system to install a package provided by your operating system vendor.