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 see upgrade pricing and information here.