If you open you iPhoto library with the Photos app it will convert it to the Photos format and all albums will be intact. The Events in iPhoto get converted into albums and will show up in a folder in the sidebar titled iPhoto Events:
Once you do that you can merge the new Photos library into your existing Photos library with the paid version of PowerPhotos and maintain all albums, edited versions, original versions and metadata you may have added in the iPhoto library.
This is what PowerPhotos can merge compared to Photos:
PowerPhotos: Photos:
Albums -----------
Smart Albums (as regular albums) -----------
Folders -----------
Captions Captions
Titles Titles
Original images Original images
Edited images Edited images
--------------- Locations
Favorites Favorites
Can detect and exclude Duplicates detect after import
duplicates or not during import
Neither method included projects.
Both methods could import older iPhoto libraries into a Photos library when the iPhoto library couldn't be migrated into a Photos library under Ventura.