Hi,

If you are using the odoo online(online trial provided by odoo sa), i think you cannot connect it via the pgadmin, as the credential of the postgres is not in our hands.

If you are using odoo installed in your own local machine or in your cloud server, you can connect it via pgadmin, as the required credentials will be in our hand itself.

For connecting the odoo with pgadmin, this link will be helpfull for someone who is looking for the same: Configure pgAdmin4

Thanks