I just didn't know how GPT vs MBR was selected as the boot type.
Ah, there is one thing more to pay attention (maybe). If you have a DVD or created a USB Stick to boot from it can boot with two modes. New boot (UEFI boot) and old style (legacy boot). On some boards you have then the option to choose between the two of them from one boot medium
or it has to be selected explicit. UEFI only/legacy only
When Windows starts this small white bar or the 'press any key to boot from....' that and the writing looks slightly different. It's really hard to tell the difference, once bootet the Windows-Wizard does not tell which mode was booted.
Example:
https://www.windowsphoneinfo.com/thread ... nu.167141/Sandisk Cruzer is shown 2x
If you have this option 2x or with the DVD-Rom, then choose UEFI for the right boot mode. Then it will write GPT,EFI etc. correct. After the first autoreboot from Windows, this 'UEFI'-Option will also appear for your sata0/disk0, but from there it should do everything automatically. Only the initial boot has to be correct, otherwise restart again.