In the Freemium version of Home Design 3D the backup is deactivated by default, so if you want to create and save a new project, you will have 2 integrated purchasing possibilities :

You can directly buy the full version (Gold),

Or buy only the backup function (Classic).
In this case you will have the possibility to create and save as many projects as you want, but you will not benefit from the whole library of 3D objects of the application which will be proposed to you by thematic packs.

Only the Gold version includes both the backup function and the set of 3D object libraries