(Sorry, got distracted; hope you don't mind my revisiting your comments.) What you say about tracking is surprising. The advice I have always seen on regular camera forums (not underwater) is to turn off tracking for wildlife photography and leave it for things like auto racing where the movements are more predictable. How exactly are you using tracking? Do you turn it on in specific situations? If so, what situations?
All good, hope you were distracted by something in the water
. I think most of the focus modes are just "try it and find out what works best for you." Single autofocus was what I used with my TG-5 and E-PL10 most of the time. Continuous autofocus is good if something is moving toward you. However, if it's moving side-to-side and also toward or away from you (e.g. a fish swimming) then tracking might help. This is especially true if you use the autofocus set to the center to start tracking on a selected critter, then use backbutton autofocus to hold focus while you move the camera around and try to set up a shot. If the critter continues to move while you are working on getting a decent background, then tracking could benefit you.
Other times, maybe not so much and it's not worth the hassle. I've been pleased with in on the OM-1, at least.
I've never been a fan of back button autofocus; splitting a single smooth movement for two functions (focus and shutter release) into two movements in two different areas of the camera body takes more time, which might be critical if a fish moves by fast, and creates more risk of camera movement it seems to me. But I have an open mind.
Back button autofocus is great if you're using tracking. After I discovered that the tracking was less than stellar on the E-PL10 and switched over to single autofocus, I just used the shutter release half-press to make it work. I agree that there's no reason to use back button autofocus in this situation. It's really challenging on an underwater housing to get enough tactile feedback to tell when you've half-pressed the shutter if you're trying to pause there, but if you just want to click and focus before the fish is gone, back-button is more hassle than it's worth.
What autofocus point customization modes are you using exactly? I could see having a pinpoint mode and a larger area mode, e.g. for fast-moving subjects (that's what I do for birds). Anything else?
Yes, I use exactly those, plus I like starting with the cross mode and adjusting the size a bit. It's helpful when things are sweeping across my field of view in one direction or another.
I tried that with two different flashlights – and got horizontal banding on my photos both times. Maybe it's because I use electronic shutter? Do you recall what flashlight you used and got good results with?
I have the Odepro WD12 that I got from Amazon for $50. It's great for night snorkels when you're just looking around but suffers from pretty substantial hot spots if you're trying to do anything even remotely wide angle using that as your only light source.
I took this with the WD12 using the TG-5 in Palau in 2022. I'm pretty sure the compact camera only has electronic shutter, not a physical shutter, right? I've never seen any banding so I don't think it's using PWM to drive the LED.