pgadmin4 package has no installation candidate

1 - Create the file /etc/apt/sources.list.d/pgdg.list and add a line for the repository

deb [arch=amd64] focal-pgdg main

2 - Import the repository signing key, and update the package lists

wget --quiet -O - | sudo apt-key add -
sudo apt-get update

3 - install posgtresql

sudo apt-get install postgresql-12 postgresql-client-12 postgresql-12 postgresql-contrib libpq-dev postgresql-server-dev-12

4 - install pgadmin 4

sudo apt-get install pgadmin4

Reading package lists... Done
Building dependency tree
Reading state information... Done
Package pgadmin4 is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
E: Package 'pgadmin4' has no installation candidate

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