The Debian install instructions have you either 'wget' weewx-python2.list or weewx-python3.list. Truth be told: either way, you get the same version of WeeWX. The difference is in the dependencies. So, if you intend to use Python 3 (and you should), you want weewx-python3.list. It will install the Python3 dependencies. Looks like that's exactly what you did.
As far as which version of Python gets invoked when you type the command 'python', well, that depends on the OS. For Debian 10, it's Python 2. However, to use Python 3, it's easy enough. Just use the command 'python3':
python3 -V
Python 3.7.3
If you use weewx-python3.list, the package installer will automatically make sure the right version of Python (Python 3) gets invoked when you run weewxd, or any of the utilities.
Hope that helps
-tk
-tk