How is it confusing? You asked how to do it from Linux. I said you can not. You have to mark the partition as system active from within Windows. I think that is pretty straight forward.
To mark the drive as boot is NOT the same as Windows seeing it as the System Active disk. That is the Linux mark if you were dual booting with Linux that flag would help you. But since you are running Windows it does nothing. That is a Linux based tag. Not a Windows one.
So get into Safe Mode and go under Disk Management and right click and mark the drive as system active.