@Carlos:I found accidentally another Linux distribution for PowerPC. Sadly obsolete, I guess.
Source Mage GNU/Linux. Version 0.9.2 is still available:
https://sourcemage.org/Download -> other versions
But they have written in 2016:
"Additionnaly, the distribution is provided with an easy-to-use basic system installer from which administrators can not only install but rebuild to their specification. It is also possible to install from alternative methods, like from a chroot. We currently support x86 and x86_64 architectures. We support ppc as well, but it's getting less activity lately."
https://sourcemage.org/Intro