Keyboard and mouse issues
Magic keyboard isn't working with powermac G4 nor is wireless mouse
Question marked as
There are a lot of PowerMac G4 variants. Still, the reason those Bluetooth devices don't work is that most G4s do not have Bluetooth capability from the factory.
Per the MacTracker database (in the Mac App Store), the only G4 PowerMacs model that could even have Bluetooth as an option was the PowerMac G4 (FW800) made for about 6 months in 2003. BT was also an option on a few iMac G4s.
You can try a Bluetooth USB dongle but most require software drivers that no powerPC Mac can run.