How can I recover Aperture picture files after migration to Sonoma?

Unfortunately macOS 12 has been the last system version, where the Photos.app could open Aperture Libraries and convert them to Photos Libraries.

On macOS 14 we can only import Aperture Libraries into an existing Photos Library. This will save the image files, but the structure of the library with the albums and folders will be lost.

Try the following:

• Launch the Photos.app and use the command "File > Import", then select your Aperture Library in the Import window.
• Photos will now show you the photos from the Aperture Library that are not yet in your Photos Library. Select the ones you want to import.

If you own a license for PowerPhotos, you can use it to create a new Photos Library from your Aperture Library, but you need a license for the full version of PowerPhotos, the trial version will not suffice.