Remove Catalina update files form High Sierra

I downloaded the Catalina (or perhaps Big Sur) update on my High Sierra system, during the install, it told me a couple of apps won't run on the new OS (I have some 32 bit apps that won't be updated to 64 bit until the summer). I need those apps to work for now, so I quit the install. But now every day I get a reminder to update, or be reminded again tomorrow. No way to opt out is given.

How can I remove the update files to avoid the pesky daily reminder?

Try doing a search for "Catalina" or "Big Sur" in Finder or delete the Install macOS [Catalina/Big Sur] from your ~/Applications folder.

Though that won't remove the reminder. That annoying little bit of Apple self promotion is near impossible to remove these days.