CHIRP depends on python2 and several other python2 related packages. These have been removed from Ubuntu 20.04
As CHIRP is migrated to python3, you can try a flatpak that is in early development in the meantime.
From https://www.flatpak.org/setup/Ubuntu/
sudo apt install flatpak
If that doesnt work then try:
sudo add-apt-repository ppa:alexlarsson/flatpak
sudo apt update
sudo apt install flatpak
Now that flatpak is installed, you'll need to set up the gnome plugin and the default repository
sudo apt install gnome-software-plugin-flatpak
flatpak remote-add --if-not-exists flathub https://flathub.org/repo/flathub.flatpakrepo
Now that flatpak is all set up try out this flatpak by Richard Shaw
curl -LO https://hobbes1069.fedorapeople.org/chirp-20200430.flatpak
flatpak uninstall chirp
flatpak install chirp-20200430.flatpak
If you already had flatpak installed, you'll immediately notice a CHIRP icon in your programs list.
If you just installed flatpak, log out and log back in to see the new CHIRP icon in your programs list.