unable to install windows on bootcamp partition + windows cannot be installed to this disk. This computer's hardware may not support booting to this disk. Ensure the disk's controller is enabled in the computer's BIOS menu.

I want use ssd in dvd/opti bay only for bootcamp windows, but cannot install W10 there because bootcamp windows installer still log report: "Windows cannot be installed to this disk. This computer's hardware may not support booting to this disk. Ensure the disk's controller is enabled in the computer's BIOS menu." Any idea for solution please?

On a 2012 Mac, with more than one hard disk, you need to install Windows in the main bay slot, while the second disk is disconnected from the Logic Board. Once Windows is a fully installed, you can then connect the Optibay SSD with macOS on it.