It’s either in this thread or the other thread on installing Linux that this is mentioned and the work around for it, if I recall correctly.
I will say this, I did get Sid installed and had all drivers working on my iBook G4 but running apt update and apt upgrade borked the install… and that is to be expected as Sid is the unstable and experimental build.
You didn’t ask but my suggestion is to try OpenBSD or Adélie Linux.
Personally, the only PPC computer I use anymore is my PowerBook G4 15” Aluminium and it runs Leopard and I run old applications like abandonware and games.
My point is you wrestle Debian Sid on to your PPC Mac, and indeed may get everything working but at some point you’ll want to install something, and that application or one of it’s dependencies will thrash your install, hence I suggest Mac OS X, OpenBSD, or Adélie.
Good luck!