If you intend to only install Postgres 11 client for Ubuntu, mainly for pg_dump and pg_restore commands, follow the steps below.
Install PG common package
sudo apt install postgresql-client-common
Install PG client 11
sudo apt-get install curl ca-certificates gnupg curl https://www.postgresql.org/media/keys/ACCC4CF8.asc | sudo apt-key add - sudo sh -c 'echo "deb http://apt.postgresql.org/pub/repos/apt $(lsb_release -cs)-pgdg main" > /etc/apt/sources.list.d/pgdg.list' sudo apt-get update sudo apt install postgresql-client-11 pg_basebackup -V
Check if pg_dump is available
pg_dump --version