If you want to install latest version of Postgres on Ubuntu 20.04 maybe you’ve tried script from Postgres website, but when installing you’ll get warnings that using apt-key is deprecated in such a case and also for me not to modify the script every time I’ve decided to write it here.

# Install the prerequisites:
sudo apt install curl gnupg2 ca-certificates lsb-release ubuntu-keyring

# Import the repository signing key:
curl https://www.postgresql.org/media/keys/ACCC4CF8.asc | gpg --dearmor \
 | sudo tee /usr/share/keyrings/postgresql-archive-keyring.gpg >/dev/null

# Create the file repository configuration:
sudo sh -c 'echo "deb [signed-by=/usr/share/keyrings/postgresql-archive-keyring.gpg] https://apt.postgresql.org/pub/repos/apt $(lsb_release -cs)-pgdg main" > /etc/apt/sources.list.d/pgdg.list'

# Update the package lists:
sudo apt update

# Install the latest version of PostgreSQL.
# Or any other version:
sudo apt -y install postgresql-16 postgresql-client-16