Not sure if you are after actual buildings rather than say items of furniture but here is a site with free 3d models of famous buildings in 3DMF file format (Quickdraw 3d file)
http://www.greatbuildings.com/types/models/detailed_models.html
Only problem is I think in the case of a Mac, you need to be running System 9 to get ArchiCAD to open a 3DMF as an object as it's not working on my OS X Mac (It says the file type is newer than version 1)
You can also convert 3dMF files into DXF or Lightwave using EI Transporter (variable results though) or use DesignWorkShop Lite and than get them into ArchiCAD that way.
AC versions 3.41 to 25 (UKI Full 5005).
Using AC25 5005 UKI FULL
Mac OSX 10.15.7 (19G2021) Mac Pro-2013 32gbRam AMD FirePro D500 3072 MB graphics