It’s the version I had, which was 32-bit, and won’t run on Catalina. But they don’t offer a comparable version any longer (standalone). Now, they all appear to be sold as annual subscriptions, which is an expensive proposition for an app that I don’t use that often. Yes, the newer versions require MacOS 12 and above to run.
If it’s the PDF Shrink app by Apago, the current version (4.9.1 build 11700) is a 64 bit Intel program. It hasn’t been updated in several years, but it remains one of my favorite utilities. It works well on my Mojave machine at home and on an M1 Mac running Ventura at work.