I looked around and didn’t find this answer at the moment, followed the Postgres how to mostly. With default postgresql-client you might get an error because the client and server have different versions, for me the server had postgresql-server-11.

So install the same version for the client following the official guide
https://www.postgresql.org/download/

# Create the file repository configuration:
sudo sh -c 'echo "deb http://apt.postgresql.org/pub/repos/apt $(lsb_release -cs)-pgdg main" > /etc/apt/sources.list.d/pgdg.list'

# Import the repository signing key:
wget --quiet -O - https://www.postgresql.org/media/keys/ACCC4CF8.asc | sudo apt-key add -

# Update the package lists:
sudo apt-get update

# Install the latest version of PostgreSQL.
# If you want a specific version, use 'postgresql-12' or similar instead of 'postgresql':
sudo apt-get install postgresql-client-11

And when done you can backup

pg_dump -d your_db_uri_here > backup_yourDB_todayDate.sql