I bought a Mac

The late PowerPC-era Macs are really fun to play with, because they're an interesting blend of modern niceties like USB and Ethernet but are limited with how old most software is. There's still a scene of people working on bringing newer versions of GCC and other *nix utilities to Tiger or Leopard, working with the pre-release PPC betas of Snow Leopard, and trying to keep online services working despite aging TLS versions and retired APIs. Compiling takes forever until it fails with an obscure C11 error or missing C library features. And that makes for a fun, if often frustrating, challenge.

But PPC32 Linux support is quickly falling off. Gentoo isn't just used because it's fun to leave your lampshade iMac G4 compiling a kernel for days, but because it's one of the few distros still supporting the platform. There's unsupported testing repos for Debian (and maybe Ubuntu?) plus the up-and-coming Adelie. Otherwise your best bet is OpenBSD - FreeBSD and NetBSD usually lack precompiled ports, and FreeBSD has announced the next major release will almost definitely drop 32 bit PPC.

The 64 bit G5 systems are much better supporte. I'm pretty sure they can boot ppc64le that many distros target. They're also even more modern - the final models had PCIe, SATA, and up to 16GB of DDR2 RAM. Sadly there's nothing modern about the power efficiency, nor the self-destructing water cooling system.