I've begun early experiments in converting from Aperture to Apple photos. I've not found any good user descriptions of the process. This post will be updated as I do experiments or use the results of experiments to refine my searches.
For my first trial I created a new project from a single JPG image and one version using Aperture under Mojave. I copied it to an Intel Air running Monterey 12.1 and opened it in Photos.
Photos said it could not open the Aperture library. It did not say why.
I then regenerated full sized previews per Apple's directions and I tried again. This time the import proceeded. I could see the Version of my original photo but not the original. I then chose Revert to Original and Photos displayed the original image. Then I tried "Undo Revert" but that did nothing. My Version was lost.
Opening the package I could see a file in the originals folder named with a GUID and a .jpeg extension. It had a size of 2.3MB which is the size of the Aperture original.
I tried to repeat the process but Photos declared that "the content of the Aperture library ... has already been migrated to Photos". The famous léonie of Apple forums explained - the conversion process changes the extension to "migratedphotolibrary", I renamed the extension to .photolibrary and I was able to repeat the import process.
On repeating I saw my Version image. I then tried to edit it and got this message:
"Cannot Start Editing Photos cannot edit this image because it uses an unsupported format"
I explored the new Photos library (Package Contents) and could not find any JPG other than my original. I am puzzled as to how Photos generated the version I could see.
There does not appear to be any way to see the original image other than by reverting to original -- which cannot be undone. There also doesn't seen to be any indication that an original exists! (This appears to be a global Photos problem however).
If one wanted to see both a Version and the Original one would need to export from the Version rendering then open that in Preview, revert to Original, then compare.