Debian Buster: install pgadmin4 (fresh postgresql 11)

1. Download apt key https://www.pgadmin.org/static/packages_pgadmin_org.pub and add key
   # wget https://www.pgadmin.org/static/packages_pgadmin_org.pub
# apt-key add packages_pgadmin_org.pub
2. Create and append pgadmin4 repository
   # echo "deb https://ftp.postgresql.org/pub/pgadmin/pgadmin4/apt/$(lsb_release -cs) pgadmin4 main" > /etc/apt/sources.list.d/pgadmin4.list
3. Run update & install pgadmin4-desktop
   # apt-get update
# apt-get install pgadmin4-desktop
   
   

By default postgres user has no password in database (not system). You need to set/change postgres database password. From root linux shell
# su - postgres
$ psql
# \password
<type_your_password>

Try login to your postgres using psql
$ psql -U postgres  -h localhost
Password for user postgres:
psql (11.7 (Debian 11.7-0+deb10u1))
SSL connection (protocol: TLSv1.3, cipher: TLS_AES_256_GCM_SHA384, bits: 256, compression: off)
Type "help" for help.
postgres=#

After running pgadmin4, pgadmin4 server will started and the first time you need to create master password (NOTE: master password is password to use pgadmin4).

Connect to your local postgresql server

1. From your browser http://127.0.0.1:41271/browser/, Add New Server
2. Fill
   
   1. Connection: localhost (your connection name)
   2. Port: 5432
   3. Maintenance Database: postgres
   4. Username: postgres
   5. Password: <your password>
3. and Save
   
   

Reference:
https://www.pgadmin.org/download/pgadmin-4-apt/