The PPA you need to add to get CHIRP is NOT an Ubuntu repository, it is Dan Smith's repository:
sudo apt-add-repository ppa:dansmith/chirp-snapshots
sudo apt-get update
sudo apt-get install chirp-daily
The problem you will run into is that CHIRP requires Python 2.7, and Ubuntuy 20.04 only comes with Python 3 by default.
You can download and install Python 2.7 in Ubuntu 20.04, but then you need to figure out how to switch between Python versions.
I looked at that and decided it was not worth it, I am sticking with 16.04 LTS.
Pat Anderson
KD7OAC