You can try installing Linux on the G5. Debian 10 "Buster" is the current version of Debian and there is an unofficial (aka unsupported) port for the PowerPC platform. This is the easiest way to install Linux on the G5, but it will have limited app support. I'm not sure it will even have a working web browser. I did install Debian 8 (officially supported version) years ago without any problems. At the time app support was mixed for the PPC software.
Here is the link to the bootable network installation .iso file which you will most likely need to burn to a CD. If a G5 can boot from a USB drive, then you can use Etcher (Mac/Windows/Linux) to "burn" the .iso file to a USB drive.
https://cdimage.debian.org/cdimage/ports/10.0/ppc64/iso-cd/
Here is a very old Debian PPC installation guide which may help guide you. While some things have changed, the basics are mostly the same.
https://www.debian.org/releases/jessie/powerpc/
Here is the Debian Administrator's handbook to help you understand Debian with tips on how to safely administer your computer:
https://debian-handbook.info/browse/stable/
Again, while it references Debian 8, most of the topics are still relevant in Debian 10 "Buster".
The only other Linux distribution I am aware of that still supports the PPC platform is Gentoo, but that OS is very difficult to install.
