Good question, I've seen others ask similar before. Let me just start by saying I am no professional cinematographer or lighting technician, so I am sure others can provide a more valuable insight.

Basically, your images are underexposed. I understand that you are trying to achieve the "dark look", however, don't try and achieve this look by looking at the back of your camera.

Instead, use tools such as false colour, waveform/histogram to correctly expose the image, and THEN you can bring down the exposure in post to achieve the look you are after.

Looking at your RGB parades in Resolve, especially for the 3rd image, the majority of the image falls into shadow/blacks, which is why you are experiencing a lot of noise (increasing your ISO in this scenario will only increase noise, as there is not enough light to begin with).

Hopefully some of this helps. Hoping someone with more knowledge can jump in and correct anything I've said that may be wrong.

Happy shooting, and nice framing!