Voici comment installer PgAdmin 4 sur Linux Mint 20 (Ulyana) :

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 install pgadmin4