Mac OS & Photoshop CS5 or newer

Your operating system is macOS, but older than Catalina. And you have Photoshop CS5 or newer. For macOS Catalina and Big Sur you have to use the installer on the main download page.

64-bit Intel plug-ins for Photoshop CS5 and newer including Photoshop CC 2018. These plug-ins only work with CS5 or newer in 64-bit mode.

MultiFill Macintosh CS5 64-bit Intel (Free)

Flatten Pro Macintosh CS5 64-bit Intel