I did several time a hard shut off while booting windows by long pressing the power button. Finally I got to the extended windows options and there to the command prompt. With the DOS commands I was able to rename the insyde folder. Now booting into windows is possible.
But the question remains how to install insyde correctly …
For future visitors of this thread, remember that you can access the OS selector without requiring a keyboard by holding volume down + power while turning the device on.