Aperture CAN work in dual-boot. OS13 and OS 10.14. I had tried without success two other methods to make Aperture work: — Method 1 using Retroactive in OS 13 (this wouldn’t show RAW images for me, even with double “reprocess originals”) — Method 2 using OS 10.14 in Parallels, which had exactly the same problem with RAW images. 

For a third, successful, method, my local tech support whiz (Technician X) set up dual-booting. Retaining OS 13.5.1 on my computer, he installed an external SSD loaded with OS 10.14, Aperture and my Aperture Library (in Pictures) all on it. OS10.14 is initiated by holding Option down during the Apple logo in startup, selecting OS 10.14 instead of OS 13). 
My computer is a 2019 iMac Retina 5K 27 inch. My RAW images are from various Olympus cameras including a 2022 one never on the Aperture camera list. 

Success!! This dual-boot does work (in contradiction to other reports that dual-booting doesn’t work on newer OS’s). 

– In OS 10.14, my Aperture now opens with the logo “Aperture (unboxed)”. It doesn’t seem relevant. Videos also work, as do audio notes recorded on my camera after shooting an image. And Books.

– RAW images first appeared with the dreaded black “unsupported format” image. [So this is not exclusive to Retroactive.]  BUT this time, when I did “reprocess originals” twice, the image was fixed and became visible. To do a lot of images all at once, it was tedious: open each and every image, wait for the black “unsupported” box, and then to the next one. I was unable to short-circuit this step. Then, Select All, “Reprocess Originals” twice, and wait for “processing” to finish all the images.

— An important thing that hadn’t worked before does work now: my old lovingly-made Aperture Books which I wanted to reprint. These had shown up in Retroactive (without RAW images) but with a major failing: pressing PRINT (top right, in the Book window) did nothing. This step is vital to be able to extract the book pages exactly as-made in order to print them in another Book program (I use Mimeo, in Apple’s Photos app.) I’ll write a separate post on how to do that if Joseph allows. Pressing PRINT now works, allowing creation of a pdf for each book page.

— I am designing new Apple books using this Aperture system. I copy adjusted versions of my photo images to Aperture from Capture One (where I now process my images). To print the book, I will transfer the images of each page to Photos/Mimeo/Create Book. Clunky? Not any worse than having to transfer all the images from Capture One to some other book-making software (e.g. Mimeo’s) which often have fewer choices of fonts and page layouts than Aperture’s books do.