Well, actually the release was announced today.

There was one bug fix which did not make it into the release but could possibly affect Python, due to the fact that Python is installed as a framework, and frameworks to not have icons.  I can supply a (1-line) patch if needed.  To test, import tkinter, create a tkinter.Tk object and open the "About Python" menu.  If the icon displayed on the About dialog looks like a folder then you need the patch.

Please let me know what happens when switching to dark mode.  My concern
arises from my understanding that python is being built with a macOS 10.9 SDK, which does not understand dark mode.  I don't know what will happen when running that code on a system which does support dark mode.  Since Tk can be build on Big Sur with a minimum target of 10.9 (and I recommend doing so) I think it should be OK. There may be warnings when linking _tkinter.so though.

I do not understand why the 10.9 SDK is needed, since I recently built Python 3.9.0 on Big Sur, with a minimum target of 10.9, and did not see any significant issues.  (Well, maybe A few warnings from the posix module need investigation.)