copy the iPhoto Library (or even the entire Pictures folder) onto your external HD/SSD or USB-stick.go to Users –> –> Pictures –> iPhoto Library.
The best way to get as much info and edits into Photos.app as possible is to do the following : But… as you already mentioned, you will loose all additional info and edits that you added in iPhoto back in the days. Of course, the easiest and quickest way to get the original photos into your new Photos.app would be to just import all the old photos into Photo.app. Or do I have to import the photos as just photos and lose all additional info and edit that was done in iPhoto long ago ? Is it possible to copy the database and open it in the Photos.app on my new Mac that runs macOS 10.14 Mojave ?
On my old PowerPC G4 (or G5) Mac I found some old photos in iPhoto.