How to import migrated Aperture library from Apple Photos to Lightroom?

Question

I'm a bit late at migrating to Lightroom. I was an iPhoto user, then an Aperture user, and when Apple killed Aperture, I switched to Apple Photos. I regret my decision.

Apple Photos doesn't meet my needs, and I'd like to switch to Lightroom. Moreover, I want to preserve as much organizational information (ratings, keywords, metadata, labels, face tags) as possible. I think this possible with Adobe plug-ins for iPhoto→Lightroom and Aperture→Lightroom, but, as far as I can tell, Adobe hasn't made any import plug-in for Apple Photos. Fortunately, I still have access to my old Aperture library from before I migrated it to Apple Photos.

Can you help me cobble together an import plan that optimizes the amount of organization data that are preserved? These are the resources at my disposal:

1. Aperture Library 1.aplibrary (7.3 MB), which I only include for completeness. It's created and last opened timestamps are within six minutes of each other two years ago. Its existence seems consistent with other users' experiences.
2. Aperture Library 2.migratedaplibrary (118.41 GB), which was born out of my ill-conceived Aperture→Photos migration and appears to be actively modified by Photos yet still readable by Aperture. The Aperture→Lightroom plug-in does not want to import a .migratedaplibrary; it wants an .aplibrary. I tried to simply rename this to Aperture Library 2.aplibrary, and the plugin didn't like that either.
3. iPhoto Library.photolibrary (7.4 MB), which I only include for completeness. It's created and last opened timestamps are within six minutes of each other two years ago.
4. Photos Library.photoslibrary (73.45 GB), the main file that gets used by Photos on a day-to-day basis.
5. A backup folder full of Aperture reference image files (195 GB)

I would usually be able to tell where all my photos reside by how big each library is, but since Apple Photos stores so much in the iCloud, I can't be completely sure. I have not downloaded all originals to my iMac, but I can.

I imagine the best outcome would be to import my old Aperture library (with metadata), import my current Photos library (photos only), and magically deduplicate between them. I imagine this is easy to screw up. The details scare me, and I'm not sure whether I can massage my migrated Aperture into being eligible for use with the Adobe Aperture→Lightroom import plug-in.

Answer 1

In May 2019, Adobe published a free Lightroom plugin for Mac to help people migrate from Aperture and iPhoto libraries. It does exactly what you want. Migrate from Aperture to Lightroom Classic on macOS.

Here is what it includes:

METADATA

Flags
Star Ratings
Keywords
GPS Data
Faces: Face naming tags are mapped to keywords
Rejects: Files designated as Rejects in Aperture are imported into Collections > From Aperture > Photos Rejected in Aperture
Info Panel metadata that can be entered in the Info panel (i.e. IPTC)
Hidden Files: Files designated as Hidden in iPhoto are imported into Collections > From iPhoto > Photos Hidden in iPhoto
Aperture Color Labels: Color Labels are mapped to keywords: Red, Orange, and so on, including support for custom label names 

ORGANIZATION

Aperture Stacking: Stacks information is mapped to keywords: Aperture Stack 1, Aperture Stack 2, and so on
Aperture project/folder/album hierarchies are mapped as closely as possible into Lightroom Classic collection sets and collections
iPhoto events/folders/albums are mapped as closely as possible into Lightroom Classic collection sets and collections
Aperture Versions translate into Virtual Copies in Lightroom Classic (without adjustments)

EDITS

You can choose to import Full-Size JPEG Previews of your edited images from Aperture/iPhoto, if they are up-to-date - This option is off by default. Lightroom Classic can automatically stack the preview with the original photo.
    Full-Size JPEG Previews generated from files that have settings don't include metadata that has been applied to the master (keywords, star ratings, flags, GPS data).
    Full-Size JPEG Previews are duplicated if imported first by the same iPhoto library and then later from a Library upgraded from iPhoto to Aperture (due to a difference in filename).