9 Things to Do Before Installing macOS Catalina 10.15.7

Check App Reviews, Compatibility and Install Updates

This update specifically removes support for 32-bit apps and there are other apps that need updates to work on macOS Catalina. If you use an app that is only available in 32-bit, don't upgrade. 

You can check out this unofficial list of apps that work and don't work on macOS Catalina to get started. You can also check with developers and with companies that you buy apps from. 

If you use a specialized tool, anything that connects to external hardware or custom software for work, you can expect bigger issues and you may not want to update yet.