If you specifically need the old v1.x branch for an older machine (e.g., running macOS 10.8 or CS6), the last available version of that branch was v1.6 , which is also available to license holders on the official site.
Many legacy projects rely on this specific version because newer builds (Element 3D v2.2) require a paid upgrade and drop support for older Mac hardware. Thus, v10345 remains the "golden build" for users with Mac Pro 5,1 or older iMacs. videocopilot element 3d v10345 plugin for ae mac osx link