After updating the OS to Catalina 10.15, I can no longer activate or add fonts to Suitcase Fusion
This issue occurs on Mac OS X 10.15 using Suitcase Fusion version 18.x.x or 19.x.x. If you're not sure of what version you're using, please see this article.
As of Mac OS X 10.15 32-bit applications are no longer allowed to run or function. Though Mac OS X lists Suitcase Fusion version 18.x.x and 19.x.x as being 64-bit applications, they aren't fully 64-bit compliant. The first Suitcase version to achieve this was version 20.0.0.
You will need to purchase an upgrade to Suitcase Fusion version 20.0.7. You can start that process here.