Can't build lighting - at all [FIXED]

I’m on OSX, just installed a completely new system with High Sierra… (GTX 1080) I have installed 4.20 and 4.21 preview 3, and I can’t build lighting on any project. Not even a blank new project with a floor and a cube, the progression stays at 0%, and then eventually stops…
Am I missing something ?

If you’re trying to run with a GTX 1080 maybe there’s an issue with hardware compatibility, since it’s not properly supported.

Well it works with 10.12.6 Sierra… And you have to upgrade to use the latest builds :-/

Turns out it’s a firewall issue (Little Snitch for me), Editor needs to accept incoming connections