You can still do things the old-school way though, by just going to the site
https://kx.studio/Applications:Carla
or add KX studio repo with the instructions from here
https://kx.studio/Repositories
I thhhink on Ubuntu, you should finish with
sudo apt-get update
sudo apt-get upgrade
so it all then shows up in your package manager
Also, Python 2 has reached end of life so that even affected DisplayCal and some others, but they say when the devs have updated their stuff, it will be added via Backports PPA
https://ubuntustudio.org/news/