Downloaded latest Ubuntu ISO
Downloaded Etcher
Installed etcher just fine on my Mac Mini Running Catalina 10.15.7
Ran Etcher
Installed a USB drive and Flashed it just fine

Installed the USB into my iMac late 2006 model running 10.6.8 currently
Rebooted holding the Opt key
The only boot option showing is the Hard drive and no USB shown
Stuck

Any suggestions?