Lost access to iPhoto

Catalina will not run the iPhoto application but you can access your photo library using the Photos application in Catalina.

See: Switch to Photos from iPhoto on Mac - Apple Support

Regarding a backup, Apple does recommend backing up before upgrading and I would highly recommend having a current backup any time, not just when upgrading. Hardware can fail with no warning, software errors can cause data loss, computers can be stolen, lost in a fire. Not having a backup of photos in a year is risky.

iPhoto was discontinued more than 4 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.

Really, panic not. But also, it's no one's fault but your own if you don't back things up.

Click on the Photos icon in the Dock, press Option, click on Choose Library, navigate to the iPhoto one(it'll be in the Pictures folder of your home folder by default), and back it up.

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Niel, why do you keep saying "back it up", it does not seem to follow from your other advice which creates a new Library.

The upgrader does not work on Catalina.

The upgrader is useful if you're upgrading v8 to v9 of iPhoto.

Perhaps if you explained the issue you're having we might be more able to help.

Would you give the workflow that you used to solve your problem so others with a similar problem can benefit from your experience?