Maybe I'm missing something but I cant get TSC to launch with DX12 in borderless only in full screen but I need to use borderless for RW enhancer (I believe that's why I cant remember for sure)
Delete the PlayersProfile bin in the content folder and let it rebuild that on a startup and see if that fixes it.
I also had the problem with DX12; I reverted to Nvidia driver versions 566 or 577, and now everything works again in windowed or borderless mode.