Photos to Aperture

The option to share photos from Photos to Aperture has been there in all earlier versions of Photos, but has been removed in Photos 5.0 on Catalina, because Aperture is incompatible with Catalina. You cannot run Aperture 3.6 in Catalina any longer, because it uses old iLife dynamic libraries with 32-bit code.

As there is no officially supported way to run Aperture 3.6 any longer, the "Share to Aperture" command has been removed from Photos 5.0. Have you used an unsupported patch to get Aperture to run on Catalina? Usually the Aperture icon will be crossed out in the Applications folder.

To transfer photos from Photos to other applications you have to use the command "File > export " and either save the unmodified originals or the edited version to a folder. Then import into the other application you want to use.

Which system version do you have installed and which version of Aperture are you using?

Where are the photos currently stored, that you want to transfer to Aperture? Are they in a Photos Library? Photos has a command in the Share menu "Share > Add to Aperture". This will import the selected photos (the edited versions) to the most recently used Aperture Library. For all other imports to Aperture use the Import command.