OpenSnitch works on the same principles as the macOS version, being a
host-based firewall that notifies users when local apps are attempting to
initiate new outgoing network connections.
When this happens, OpenSnitch will display a popup, asking the user for
instructions on how to deal with this new process.
All user decisions are saved as rules in local JSON files. Users can edit
these rules later to fine-tune the firewall or import/export rules from/to
In action on Mac https://youtu.be/M7Y5CtFK5Us
Easier said than done but it will pay off.