Catalina marked the end of 32-bit apps for macOS, something Apple had provided over a decade of transition help with and two years of warnings about for consumers. Nonetheless, people with older apps they hadn’t launched in a long while were still taken by surprise, judging by email from readers and forum posts.
Macworld offers a guide on how to find outdated apps to figure out what to get (if anything) to replace them, both before you update to Catalina and afterwards.
However, if you no longer need an app that can’t launch in Catalina, you’re not obliged to get rid of it. Apps, launch agents, daemons, helpers, and other components no longer work, but they won’t do harm. And it might be a mistake to delete apps that only have modules that aren’t yet 64-bit compatible.
