I can only find downloads back to version 10 online.
You might have to contact your local Archicad distributor.
Or find someone local that has been using Archicad (MAC version) for some time and may still have the installation discs laying around.
The problem is this software is almost 20 years old now and I don't think it was ever delivered digitally.
So finding someone with the installation discs may be your only hope.
One of the forum moderators. Versions 6.5 to 25 Dell XPS- i7-6700 @ 3.4Ghz, 16GB ram, GeForce GTX 960 (2GB), Windows 10 Dell Precision 3510 - i7 6820HQ @ 2.70GHz, 16GB RAM, AMD FirePro W5130M, Windows 10