idroot published a tutorial about installing Python 3.9 on Ubuntu 20.04 LTS.
How To Install Python 3.9 on Ubuntu 20.04 LTS
In this tutorial we will show you how to install Python 3.9 on Ubuntu 20.04 Focal Fossa, as well as some extra required package by Python
How To Install Python 3.9 on Ubuntu 20.04 LTS - idroot