I have a Mac that cannot be upgraded from High Sierra to Mojave because of the graphics card. While I am happy to exist on High Sierra for now, I would like to upgrade to the latest version of the Photos.app to take advantage of any improvements there might be.
Would this work or did they lock it into requiring Mojave?
In the past, you could run mixed versions of iPhoto and other OSX/macOS applications on various macOS builds. Unfortunately, once a new version of macOS is released nowadays I gather you can't even run Chess.app or Calculator.app without matching the OS version!