The post above you says what to do.
- Install Xcode.
- Open Xcode, agree to license and then close it.
- Download ioquake3 source code ZIP. Click the zip in Finder to unzip it.
- Open Terminal app. Run
cd Downloads/ioq3-master
in Terminal to change to directory containing the ioquake3 source code. - Then, still in the Terminal, run
./make-macosx.sh x86_64
. It will compile ioquake3. You can close the Terminal when it’s finished.
There should be an ioquake3 app in Downloads/ioq3-master/build/release-darwin-x86_64. Move the ioquake3 app to a folder containing baseq3.
For example:
/Applications/ioquake3/ioquake3.app
/Applications/ioquake3/baseq3/pak0.pk3
/Applications/ioquake3/baseq3/pak1.pk3
/Applications/ioquake3/baseq3/pak2.pk3
/Applications/ioquake3/baseq3/pak3.pk3
/Applications/ioquake3/baseq3/pak4.pk3
/Applications/ioquake3/baseq3/pak5.pk3
/Applications/ioquake3/baseq3/pak6.pk3
/Applications/ioquake3/baseq3/pak7.pk3
/Applications/ioquake3/baseq3/pak8.pk3