If you pay to use it then you can use later Python versions. Pro supports at least up to 3.10 as of this writing and is continuously updated for later versions.

My biggest concern would be lock-in to the license, not lock-in to an old Python version. The nominal cost to get up-to-date right now doesn't guarantee me perpetual updates, right?

I'm also suspect of the misleading presentation on the landing page; nothing in the "Open Source" section says anything about the fact that the author has resolved to let the Open Source version effectively die, while up-selling existing users to the paid version. I respect the approach, and you deserve to be payed for the work, but it would be good to not effectively lie on the home page.

thanks for the clarification