> That wouldn't help in that case as exfiltrated data is committed to public GitHub repositories

Correct in general that it doesn't protect against stuff like that. But this whitelisting is done per-command (in this case, the whitelisting is scoped to the node executable). I've had no need to allow node access to Git in the first place, so no problem there.

> Unless you have to accept every time an app posts or requests data from known hosts?

OpenSnitch doesn't have access to application-level information, so it has no concept of "post" or "request." It's got DNS names, layer 3 info, layer 4 info, and other such things that are visible to the kernel. Your rules get matched to network traffic based on these various properties.