32 v 64 bit iPhoto

iPhoto was discontinued several years ago and replaced with the Photos App. There is no 64bit version of iPhoto, so no way to use it on Catalina.

You need to migrate your iPhoto library to Photos. Look for this icon on the dock of the Applications folder in Finder:

Normally, just opening the Photos App the first time, should prompt this action if it has not already been done.

Otherwise see here for how to migrate your iPhoto Library to Photos: Updating from iPhoto to Photos for macOS - Apple Support

There is no Catalina-compatible iPhotos app. iPhotos was replaced by Photos app. It should be shown in your Dock. If you don’t see it there, look in the Applications folder. There are significant differences between these apps, so have a look here:

https://support.apple.com/guide/photos/welcome/mac

When you launch Photos, it will automatically migrate your iPhotos library to a Photos library. After you confirm that everything migrated properly, you can delete the iPhotos library file from your User > Pictures folder, but it won’t save you much disk space.

iPhoto was discontinued 5 years ago. It is no longer developed or sold. It was replaced by the more powerful (and free) Photos.app that comes with the OS. You can migrate to that app very simply:

Hold down the option (or alt) key and launch Photos. From the resulting menu select 'Choose Library' and point at your iPhoto Library. It will do the rest.

If you prefer not to use Photos there are several 3rd party apps that you can use. Which to choose depends on the kind of photographer you are and your budget.