1. Extract the zip file and place the folder somewhere convenient 2. Open Blender. Go to Edit>Preferences>File Paths>Asset Libraries 3. Click “+” and navigate to the folder “PBG_2”. Select it. 4. Set “Import method” to Link 5. Done!

Missing Manifest appears when you try to install PBG2 as an addon. It is not an addon, but an asset library. See the FAQ about installing, or the Documentation about Getting Started, for detailed setup instructions.

I have not tested 3D printing the models, so I can't guarantee it. However, you can convert the buildings to regular meshes so as long as you are comfortable with preparing meshes for 3D printing it is probably possible.