I would like to know if it is on the roadmap which python versions are going to be used in the next upgrade of ArcGIS Pro, Enterprise and Portal. For example is it already known if 10.9 is going to use Python 3.7 or 3.8?
Pro is of immediate concern
I suspect arcmap will stay on the maintenance version of python 2.7.xx. There are too many organizations who haven't prepared for arcmap's ultimate demise. But the product lifecycle goes to 2026 currently
Pro looks like they are preparing for python 3.7, which is a bit of a disappointment since 3.9 is coming to its first stable release and at version 3.8.6
In terms of ArcGIS Enterprise, it has both Python 2.x and Python 3.x bundled with it. The Python versions for ArcGIS Enterprise tend to mirror those of the corresponding ArcGIS Desktop releases. For example, ArcGIS Enterprise 10.8.1 has Python 2.7.18 (ArcGIS Desktop/ArcMap 10.8.1 has Python 2.7.18) and Python 3.6.10 (ArcGIS Pro 2.6.1 has Python 3.6.10).
I can't imagine that Esri will update ArcGIS Desktop/ArcMap to Python 3.x, which introduces several questions that others have already raised. For example, if there is a large security exploit that is found in Python 2.x, how will Esri handle it given Python 2.x has been retired. Not updating ArcMap to Python 3.x means Python 2.x needs to continue being deployed with ArcGIS Enterprise too. Etc, etc, ....
As Dan already mentioned, Esri finally seems to be serious about getting off of Python 3.6.x; unfortunately, that seems to be to 3.7.x instead of 3.8.x or 3.9.x. Once Pro makes the next step, the corresponding ArcGIS Enterprise release will jump with it.