Windows 8 GPT

On a 2011 Mac, which has a built-in Optical drive, your BC Assistant should have two options - Download and Install.

• Download - will download Bootcamp drivers to a USB2 flash drive. Do not use a USB3 storage device.
• Install - partitions your internal disk, and uses DVD installation media to install.
• Do not manually create a partition using Disk Utility, otherwise you will see the GPT vs MBR error.
• Your Mac does not support EFI Boot of Windows. Your Mac only support legacy BIOS (specifically CSM-BIOS).

Also, see Bootcamp User Interface - Apple Community for reference.

Quit BC Assistant. Insert the W8 DVD and post the output of

diskutil list

from macOS Terminal.

I don't use Windows or Boot Camp, but IIRC you should be able to use Boot Camp Assistant to install Win8 on your Mac. It may depend on which version of macOS you are using though. Boot Camp Assistant creates a custom version of the Windows onto a USB stick installer which includes Apple drivers for your Mac which you then use to install Windows. Here is an Apple article with links to instructions for installing various versions of macOS:

System requirements to install Windows using Boot Camp for macOS - Apple Support

AS024 wrote:

Is sierra free? And are you sure It will work?

https://discussions.apple.com/content/attachment/1dbe17c6-ce5a-4cca-8f00-b5e516f1ddd8

Yes. See How to get old versions of macOS - Apple Support for reference.

You cannot install Sierra, unless the disk has been erased. High Sierra will not open an older installer.

• Back up your Mac with Time Machine - Apple Support
• Erase your entire disk, not just Macintosh HD, in Internet Recovery
• Install macOS Sierra
• Install W8.1
• Upgrade Sierra to High Sierra. Be aware that repairing can be a challenge, if you choose to upgrade to High Sierra.

On a 2014 iMac, I run macOS Sierra and W10. I have used W7 on a Sierra Mac. I personally do not like High Sierra because of the broken APFS layer. I prefer Mojave, if I want to use APFS.

Do you have a USB disk which is mounted at "/Volumes/Mac\ Sierra"? Be aware that the USB disk will be erased/formatted.

You may have missed a step in How to create a bootable installer for macOS - Apple Support.

The macOS 10.12 installer is broken when using it to create a bootable macOS USB installer. Instead of fixing the issue Apple decided to hide the Sierra installer instead (it has been broken for over a year now). This command must be run in order to fix the installer:

 sudo  plutil  -replace  CFBundleShortVersionString  -string  "12.6.03"  /Applications/Install\ macOS\ Sierra.app/Contents/Info.plist

After running this command the OP can run the command in their screenshot which should now work assuming their USB stick is labeled "Mac sierra".

Please post back, I you run into any issues.