$ sudo curl https://www.pgadmin.org/static/packages_pgadmin_org.pub | sudo apt-key add

$ sudo sh -c 'echo "deb https://ftp.postgresql.org/pub/pgadmin/pgadmin4/apt/focal pgadmin4 main" \
  > /etc/apt/sources.list.d/pgadmin4.list && apt update'

$ sudo apt update


$ sudo apt install pgadmin4-web 
$ sudo /usr/pgadmin4/bin/setup-web.sh