Iphotos gone?

iPhoto was discontinued 7 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.

Launch Photos with the option key held down. From the dialog, choose your iPhoto Library. Photos will create a new Photos library from your iPhoto media.

I said launch Photos, not iPhoto, the flower petal icon:

Also, is your iPhoto Library in your Pictures folder?

If you start with the option key held down, there is a pop-up dialog, not a drop down menu.