MacOS Catalina does not allow any applications that are not Optimized to run. We found this workaround helpful. Just go into Parallels before updating and create a new virtual machine, just like you would for Windows, but install Mojave. Then you can run Mojave on Catalina, and thereby any old app.
This PC Mag article explains how to create a Virtual Machine in Parallels and install Mojave to run on Catalina.