Check requirements at https://pgmodeler.io/installation.
You will need Qt 5.9.x installed, full XCode installed, and homebrew installation of postgres and openssl.
The example below is v10.5 of PG and v5.9.6 of Qt, modify accordingly. Also, replace {{USERNAME}}
with you Mac username.
The installation is the same as the instructions at the link above. There are a few path differences due to homebrew installation locations.