Are you on Ubuntu 21.04 or newer? This package does not exist in older versions of Ubuntu, but if you are on an older version then the RPi.GPIO will be what you need. It can be installed with sudo apt install python3-rpi.gpio and there are many tutorials out there for it.
If you are on 21.04 and still cannot find this package, then you may not have universe packages enabled and updated. Can you ensure the line deb http://ports.ubuntu.com/ubuntu-ports hirsute universe exists in your /etc/apt/sources.list file and run sudo apt update? That should resolve the issue if you are in fact on 21.04 or newer.
The reason to use lgpio instead of RPi.GPIO is because of some changes in the newer kernels. More info about that can be found in the link to Dave Jones’ blog in the tutorial