How to install pgAdmin 4 on Linux Mint

1. Open terminal and type:

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

2. Open Software Sources and click on "Additional repositories" and paste the following for Linux Mint 19 (it's based on Ubuntu Bionic):

    deb http://apt.postgresql.org/pub/repos/apt/ bionic-pgdg main
   

   or the following for Linux Mint 20 (based on Ubuntu Focal Fossa):

    deb http://apt.postgresql.org/pub/repos/apt/ focal-pgdg main
   

it should look like this:

Press "OK" and that will automatically update cache.

3. Now open terminal and type the following:

    sudo apt update
    sudo apt install pgadmin4
   

That should install pgadmin4.