Catalina upgrade and iPhoto incompatibility

Hi

I know this has query been asked in a variety of ways so I hope people don't mind me re-asking but it is for clarification.

I just upgraded (very late) to Catalina from Mohave and now cannot open iPhotos. I know iPhotos has been retired by Apple but I just want to check, have my iPhoto pictures automatically migrated to Photos or do I need to do something to get them to transfer? If so, what?