Nothing special here when it comes to the post processing....one exposure in camera and in Photoshop basic adjustments (shadows, highlights, contras, whites etcetera), some use of radial filters, subtle adjustments to some colors and white balance.Those clouds are amazing!! What did you do for processing, please? Lovely shape, thoughtful image, and a "Wow!" sky.
So in addition to the 10 stop ND, does the High Res mode mean your 6 second shutter speed is multiplied by the number of spices level shifts by IBIS? Is that why this looks so smooth too?