AC 9 will run on your Intel Mac (in Rosetta emulation mode), but I believe the installer will not. So, you need to install on a PPC Mac (G4 / G5) and then copy the application folder from there over to your Intel Mac...or...
There is a downloadable copy of the US version of AC 9 on the GS web site for use in converting old files, but it does not include the library as I recall::
http://www.graphisoft.com/support/archicad/downloads/Fileconverter.html
The library can be downloaded here:
http://tr.graphisoftus.com/
Karl
One of the forum moderators
AC 28 USA and earlier • macOS Sequoia 15.2, MacBook Pro M2 Max 12CPU/30GPU cores, 32GB