Using BootCamp and insalling it on second drive of system.

Ok already tried I get cant find boot drive error.

I'm suggesting you put the Windows USB installer (created on a PC) into the iMac and boot from that. So you'll be running a bog standard Windows installation onto the internal SSD. Hold down the Option/Alt key to choose the USB stick as the boot disk.

John this is a dual boot setup, it is not running BootCamp. This works too! But you can’t flip between access of each without rebooting.

BootCamp allows you to share data files. As an example for a time there was more effective audio composing and DJ tools in Windows, yet better animation tools in macOS. So many Pros needed to jump between.

Correct Dan. It works and you don't need to buy an Apple SSD!! Who would seriously do that? There are plenty of other ways to exchange files between MacOS and Windows without using BootCamp (use ExFAT formatted partitions or USB drives). BootCamp was probably only created because it was so difficult to add extra drives to the iMac—Windows will only boot from an internal drive. Since the OP has multiple drives there's no need to use it. I use VMware to run old software in Windows XP and it's great - don't even need to reboot but having Windows on it's own drive is much more reliable and versatile. The Windows system doesn't rely on the MacOS to keep working, you can even move the drive back to a PC and it'll work.

@John - True an external drive can shuttle files across two discreet systems!

The rub here is within a single system having to reboot between the two environments takes time and if you forget something it can be tedious flipping between!

As far as Apple blade SSD this is needed only internally that’s a hardware limit within the older systems which used Advanced Host Controller Interface (AHCI) blade SSD’s like this one if you use it as the boot drive with non-Apple PCIe/NVMe drives with the newer APFS file system which is now required newer than Mojave.

Basically, this series needs a AHCI blade drive if he wants Dual boot from it as the systems firmware won’t allow MS Windows to boot from a PCIe/NVMe drive internally.

The ssd adaptor works fine. I can boot and run of the drive with no problem. Im having problems with boot cam not letting me make a install disk. Also when I made one on the PC it gave me boot drive not fount error

@Michael Galano - Why did you use a PC? That will mess up the Mac file system if you want to use BootCamp as the primary partition must be either HFS+ or with the newer OS’s APFS.

Clean the drive off of all the partitions and start again formatting the drive using macOS and install it. Make sure it works and you are booting up under that drive. Then setup BootCamp following Apples guide on this drive.

But what's the point of using BootCamp? - no need if you have two drives. Use the Alt key to choose which system disk to boot from.

@John - Are you confusing dual boot with BootCamp?

You may want to read up on what BootCamp is as well as what a Virtual Machine (VM) is. These run on top of a different OS Vs running independently with a dual boot. I have a multi-boot system which runs MS-DOS, MS Windows and Linux. Within a single drive each sitting in a different partition.

Here BootCamp sits on top of macOS in a special folder and you have a second volume on the drive to hold your windows files. If you want you can add more drives to hold your stuff (Data Files) in the same way you can within MacOS or even MS Windows! But that is not where Windows the OS files sit.

@danj - no I'm not and I've used Bootcamp, VMware, Parallels in the past - and I can tell you a standalone Windows install is the best solution.