Good evening gentlemen, I'm having the exactly same problem with my G5, so I'm following along. I too only have access to a Windows PC, and no DVD burner, only USB sticks. Not working for me either, for now. Here's what I have tried (unsuccessfully) so far
* Burn Sorbet Leopard to USB stick with Balena Etcher, who complains the image is not bootable, and TransMac. This image does not show up as bootable in Open Firmware. Tried to convince OF with setenv boot-device ud:2,\\:tbxi followed by mac-boot. The USB light flickers for a couple seconds and I am back in the flashing "?" folder screen
* Burn the 10.5.8 Leopard .dmg to USB stick with both TransMac. This image _DOES_ show up as bootable within Open Firmware yay! typed mac-boot, USB light flickers a couple seconds, back to the flashing "?" screen. Oh well
I got both dmg files from Macintosh Garden. The 10.5.8 is download #34 which seemed to fit into a 8GB USB stick, whereas Sorbet Leopard went into a 32GB stick.
Would love to read any insights from such a confederacy of distinghished gentlemen (and ladies I reckon?)
Thanks! Luca from Italy
See specs below
View attachment 1917454