Where are the sidecar files AAE for the Photos app located in Macs?

Photos for Mac does not store the edits in sidecar files. You will occasionally see sidecar files in the Masters folder inside the Photos Library, but only for photos that have been synced to the Mac from an iPhone with camera filters applied (from older versions of iOS). But the adjustments applied in Photos on a Mac are stored in the database files in the photos library, not in separate .AAE files.

Photos uses also AAE sidecar files, but only when exporting originals, that have been imported with AAE sidecar files from an iOS device.

• For example, after exporting an older iPhone photo, that came with camera filters applied, with "File > Export > Export unmodified Original, I am seeing these three files exported:
  • The original image file, a .jpg file
  • The sidecar with the filter information, .AAE
  • The sidecar with the IPTC data, an .XMP file.

In Photos 3.0 on High Sierra I used to see the imported sidecar files in the Masters folder, together with originals in the same subfolder. On macOS 10.14 Mojave the imported sidecar files seem to have been moved to a separate subfolder of the Photos Library; I am seeing them now in the subfolder "Attachments":

Searching the subfolder "Attachments" for ".AAE" of my test Photos Library revealed these files: