Boy have I been living under a stone, I wish I had known Little Snitch 2 decades ago (:
Little Snitch is a host-based application firewall for macOS. It can be used to monitor applications, preventing or permitting them to connect to attached networks through advanced rules. It is produced and maintained by the Austrian firm Objective Development Software GmbH.
At the time of writing, it was at version 5.x, and it was introduced early this century.
Site and other links:
The Wiert Corner - irregular stream of stuff 