At 1/800sec and f29, you’re not getting a lot of light for the darker parts of the image, so they’re noisy. ISO 400 was probably making you expose this way, along with straight-into-the-sun. Ah noticed you have Active D-Lighting = Auto, which also reduced your exposure a bit.
Anyhow, standard raw processing, scaled the data to fit black/white, did a curve to add contrast to the lower tones, then a rather aggressive wavelet denoise. Resized to 1080 on the horizontal and min sharpened, because that’s just what I do for reduction resize.
Shooting into the sun is challenging, you just need to let the sun go to oblivion and try to get some signal in the darker parts of the image. A custom curve of your own making is usually in order to put contrast where it’s needed, in my limited experience.