A Unity ID allows you to buy and/or subscribe to Unity products and services, shop in the Asset Store and participate in the Unity community.
Separate names with a comma.
Use the exact version of Unity specified in the tutorial, I used the latest beta 2019.2.0b5 and it didn't work, however, it did work for me with...
As with 99% of all Mac problems, this one can be resolved by repairing disk permissions with the Disk Utility.