I am using Little Snitch 4.0.x for macOS, however the more I use it, the more trouble I have got.
For completeness, I am briefly explaining my issues. It seems Little Snitch have some bugs. To not get into much details, some websites doesn't work on one web-browser, but work for any other, despite no rules being set or asked. Other issues I have got with Docker, several scripts fails to connect to simple hosts such as GitHub or Ubuntu without any rules being asked (as for workaround, adding manual rules for all processes seems to work), and now since couple of days I cannot download full images, due to network issues (Service Unavailable), but I am sure that is not the case since I have tried on several networks, and nobody else has the problems which I have. Of course, I have reported the bugs, but not received any meaningful help in order to debug these kind of problems.
So I am looking for alternative firewall for macOS (High Sierra and above), to just work as expected with similar features to Little Snitch.