Please upgrade to Photos.

Correct. 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.

The migration to Photos should be done before upgrading to Catalina, if possible: Updating from iPhoto to Photos for macOS – Apple Support

it is easier to prepare the iPhoto Library for the migration while still running a system, that supports iPhoto.

• We can search the iPhoto library for media items, that need converting to a different format, because they are using legacy codecs
• We can look-up the old descrescriptionsl of albums and projects, that will not be migrated to Photos
• We can add missing locations before migration or finish projects.
• We can compare the old iPhoto Library to the new Photos Library.
• The old iPhoto Library Upgrader will no longer ru on Catalina as well, so we will not be able to prepare old iPhoto Libraries (iPhoto 7.1.2 or older) for the migration, once we are running Catalina. (iPhoto '11: About the Library Upgrader)

The. same applies to Aperture users. Migrate your Aperture libraries to Photos or Adobe Lightroom Classic - Apple Support

It is essential to create full sized previews of the edited versions while still running Aperture