kalman

If you installed impish (the first comment), you will need to remove that file, install focal, then update and install. 

sudo rm /etc/apt/sources.list.d/impish-security.list

echo "deb http://security.ubuntu.com/ubuntu focal-security main" | sudo tee /etc/apt/sources.list.d/focal-security.list

sudo apt-get update
sudo apt-get install libssl1.1