My two cents worth. I ended up shooting in modes I did not expect when I was shooting point-n-shoots underwater. (Before getting a DSLR underwater). The reason is that there are so many variables to control that you normally can't let the camera choose for you.
Setting some program mode will probably have you end up with a shutter speed that is too slow. I find I need to get to 1/160th to avoid motion blur, either from the subject or the camera moving. Thus I've shot in Shutter Priority mode or Manual.
I want to set the aperture I need, not one that the camera picks to allow more light in. For instance, I may need F8 on wide angle or F16-32 on macro shots for adequate depth of field or for better corners.
I want to set the ISO to the lowest value to maximize dynamic range.
Setting shutter, aperture and ISO manually means that I have to vary the lighting to get proper exposure. I used to shoot in TTL, but I've found that tends to overexpose delicate details. And since I can't now shoot in TTL anyway with my D850, I'm setting the strobes to manual mode and adjusting power manually. Not as hard as it sounds as I normally dial in for macro at a certain lens-subject distance and vary from there.
If I shoot wide angle, things are different since I usually have to allow at least some ambient lighting. ISO's tend to be up in the 400-800 region, and white balance is more an issue than with macro.
For sure shoot in RAW mode.