Currently, the "Download All" feature for the entire D5 library is typically reserved for enterprise users or specific educational licenses. For the standard free or pro user, the library is meant to be downloaded on-demand.
D5 Render offers thousands of free models and materials. To make them offline-ready: Filter the library by the tag.
If the built-in library isn't enough, you can expand your offline collection by importing free assets from third-party sites. D5 Render supports .fbx , .obj , and .skp files natively.