Best photo edit program

Have you tried to update iPhoto to version 9.6.1, as described here?

Can't Update iPhoto because it is not… - Apple Community

You can only update iPhoto, if you own already a version, that is tied to your AppleID at the AppStore.

iPhoto 9.6.1 will run on macOS 10.11 El Capitan, but not on the most recent system version macOS 10.15 Catalina. The update to El Capitan may just have removed iPhoto from the Dock, but it should still be in your Applications folder. Is iPhoto crossed out in Applications?

I use PhotoShop Elements for Mac. I used to use Photoshop but with Catalina PS wouldn't work, too old. PSE does nearly everything PS could except convert images to CMYK color mode for printing by high end printers. I like it because it allows removing backgrounds easily and people from images like here:

PSE 2019 is 64 bit and fully compatible with Catalina. I use PSE from within Photos as an external editor with the  99¢ External Editors For Photos from the App Store.  This user tip shows how: External Editors in Photos Are Here

However, you should give Photos another try because it's editing capabilities are much greater than iPhoto's.

The best one? Adobe Photoshop. It's the most capable. However, for most photographers it's overkill. If you were happy with iPhoto then Photos is the ,ore capable, but not such a big learning curve - it's broadly similar to iPhoto.