Windows 10 Installation on iMac (27-inch, Late 2012) with a 3TB hard drive

Hello Everyone: so I have an iMac (27-inch, Late 2012) with a 3TB hard drive running Mojave in our office. The staff person using the machine is being reassigned to a project that requires Windows 10 to be installed on this computer. As I go to install Windows 10 via Boot Camp I find out that this one specific iMac out of all the iMacs is not compatible with Boot Camp!!!

Is there anyway to downgrade the Mac OS to a pre-Mojave version to be able to install Windows via Boot Camp?

Any help with this matter is greatly appreciated!

Thank you,

Max