Due to the fact that some things are missing in Linux on the PPC platform, it won't work correctly, for example, OpenGL, etc. I would recommend reinstalling macOS X 10.4.
If you have reinstalled Mac OS X 10.4 (PPC), you can use this client without needing to add anything extra: https://github.com/andreiixe/ClassiCube-PPC. It works pretty well and fine, but it's your choice in the end :)