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This is a machine having an Intel Core (2) Duo 64 bit processor (I think it's Core Duo without the "2"), but does only have a 32 bit EFI. So you can't use a regular boot loaders and install media to install and boot from this machine.
In addition there is the problem that, if you manage to accomplish a (32 bit) EFI install, it breaks the AMD GPU drivers. The Linux kernel will only run properly when using nomodeset which leads to further problems (missing accleration, energy/heat management, quicker hardware breakage).
So, you need a legacy BIOS/MBR bootloader, install the OS the same way (most installers will do that if you have booted the install medium that way) and it's going to work! You may even use a 64 bit OS then.
This page contains everything you need to know about installing Linux on such a machine:
Linux 2006 iMac 5.1, Markdown page on GitHub
This page contains a tutorial and software to create boot media having cut of the 64 bit EFI bootloader so the machine is going to use the MBR boot way:
Matt Gadient: Linux DVD images (and how-to) for 32-bit EFI Macs (late 2006 models)
The content on this site is licensed under CC BY-SA 4.0.
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