Which Ubuntu for Kivy and Python3

This bug, which I confirmed in Ubuntu 18.04, is probably the reason why python3-kivy was dropped from the default Ubuntu repositories in Ubuntu 19.04. This bug has been fixed and python3-kivy has been restored to the default Ubuntu repositories in Ubuntu 19.10 and later.

A later version of Kivy 1.11.1 (instead of 1.9.1) can be installed with pip3 install kivy in a Python virtual environment using Python 3 virtual environment creator (python3-virtualenv) from the default Ubuntu repositories. Try running python3 -m pip install --upgrade pip before pip3 install kivy to upgrade your pip3 to the latest version as I did.

Below are the results of running the Hello World test program from the link in your question with Kivy 1.11.1 in a Python 3 virtual environment. The Python 3 code ran without any errors, detected OpenGL and my NVIDIA proprietary graphics driver, and output this window: