Don’t get me wrong – everything new I do now is coded in 3.9 –  this is a hobby site and we move with the tide for fun.  But if money is involved, 3.5 was just a version early and so, 3.6 has replaced it on the header

Here is my reasoning:

After a couple of years of looking at and working with functionality.  I came to the realization that if I were starting a new multi-gazillion dollar project based on Python, 3.6 is far-and-away the most logical choice. F-strings made Python a real professional tool.  Nothing truly significant other than deep geek stuff or very superficial stuff has been introduced since.  3.6 is now time tested, dependable and stable enough to bet big money on.

While my free standing, on-call version of Python on my computer is 3.9.  I keep Anaconda environments available for 3.8 and 3.6 – not wasting time on anything earlier.  Time is life and life is to short as it is.