There is bug in Mac Excel which prevents connection between Excel and Supermetrics.
Microsoft is aware of this and many other services are affected by it as well. For now, there are two options:
-Use Data Grabber with Windows
-Downgrade your Mac Excel with these instructions: https://support.office.com/en-us/article/how-to-go-back-to-office-2016-for-mac-15-xx-versions-from-16-xx-e88ed6c8-6fb4-40a1-9540-529000d3d20f
We'll update this article once we have received news from Microsoft.