Help with Bootcamp

I’m trying to use Bootcamp on my Macbook Pro Early 2011 to dualboot High Sierra and Windows 7. But if I try to make an installer that uses GPT partition table it tells me that the disk must be formatted or refuses to boot. (Shown on the picture.) But if I try an installer that uses MBR it doesn’t even show up in the boot selector… What did I do wrong?

I’m trying to use Bootcamp on my Macbook Pro Early 2011 to dualboot High Sierra and Windows 7. But if I try to make an installer that uses GPT partition table it tells me that the disk must be formatted or refuses to boot. (Shown on the picture.) But if I try an installer that uses MBR it doesn’t even show up in the boot selector… What did I do wrong?