I did some searching and did not find a thread related to this (there's one called A6700 Settings about video) so I thought it might be nice to create a thread for those shooting the A6700 to discuss best practices settings etc.
I'm shooting in a Nauticam housing with a Smart Turtle TTL Trigger I'm currently shooting with YS-D2 strobes and using either the 16-50 kit lens or the 90mm 2.8 macro depending on situation.
I've only done one trip so far with the setup (I used mostly the same setup with my a6500 from 2018, so it's fairly similar)
I usually start with TTL flashes as I find I get pretty decent results that way but if the critters aren't shy will switch to going manual as I can. One frustration I'm finding right now is there doesn't seem to be anyway to just turn off the flashes in the camera, and as such I can not in Program mode use the knob to shift the aperture/shutter speed values while maintaining exposure. (Going to the flash settings and selecting Off says it's not available in this mode)
I'm shooting in RAW Mode, I select the Auto Underwater White balance as a starting place, and then am shotting in either Aperture priority or Program mode usually using a center balanced metering mode and a center tracking focus using the back button to focus at all times (I turn of focus on shutter). I tend to use focus peaking and DMF as my focus mode as it allows me to see when eyes are in focus a little more easily.
My other frustration is that with the 16-50 lens, on the A6500 in DMF you could hold the focus button down and move the knob that actuates the zoom and it would actually adjust focus, letting go of the focus button it would revert to actuating the Zoom, unfortunately on the A6700 they changed this behaviour and I now have the C3 button set to toggle between manual and auto focus modes so that I can manually adjust the focus (handy when I'm running a macro diopter on the lens)