iPhoto is by now yesterday's snow. The development stopped five years ago, when Apple stopped selling iPhoto from the App Store and new Macs came only with Photos instead of iPhoto.
You have probably missed the announcements. But when Catalina has been released last year, there have been several warnings about the incompatibility of iPhoto with Catalina because of the 32bit code, that is no longer supported, right on the top of this forum.
You should be able to open your iPhoto Libraries in the Photos for Mac application. It is a part of the system and the successor to Photos.
See: Updating from iPhoto to Photos for macOS – Apple Support
Photos should automatically open your last used iPhoto Library, when you launch Photos for Mac. If that does not happen, drag your iPhoto Library onto the Photos icon in the Dock.