I have had this same issue and went back and forth with Epic troubleshooters. Apparently it starts at Mac OS 10.13.5 or higher. I have a Macbook pro running 10.14.2 Mojave and had to go to the engine version tab and select “Verify” and it initialized, then eventually verified Unreal and now works. So if your Graphics card doesn’t have an issue with a higher OS version, that may be your easiest fix. Good Luck.