Mac pro 2006 can't use recovery mode

I want to install macOS to a hard disk for mac pro 2006(Nothing installed, no any other storage that macOS installed, but I have a working MacMini 2018).

So, I tried to use MacOS Recovery Mode and Held Command+R or Shift+Command+R

But, It doesn't show anything with grey screen and after few seconds then It shows blinking Questionmark with folder.

Can't change boot device with Option key when startup

also, Netboot with N didn't work.

I did NVRM and SMC, RTC reset.

The firmware password is not activated.

Most boot key combination shows only grey screen

(except N(blinking earth), T(Firewire icon))

Most solutions on internet didn't work for me :(