Mojave said an app needed updating. Now Catalina won’t run it

Apple announced years ago it’d end support for 32-bit apps; everything is 64-bit now. That means macOS X 10.15 can’t run 32-bit apps. The only solution is to install macOS 10.14 Mojave or earlier using Parallels Desktop or VMware Fusion and run your 32-bit apps within the virtual machine.