my AFon button to AFarea+AFON set to 3D tracking; tracking mode- animal; shutter release to wide area AF large; focus point persistence- auto; focus lock to 3 subject erratic; fn1 to Afarea +AF on (single point) for precise focus and fn3 same as fn1 to help in portrait orientation.I have my Z9 currently set to use Wide Area Large (without needing any other button pressed to select it). I use the shutter release button to initiate AF. I have the AF-On button programed to select 3D only, so the AF On button does not also start AF.
Just tried this set up inside the house (it is 0 degrees F outside). I focused on an object using Wide Area Large and the shutter release button pressed halfway. Leaving the shutter button pressed halfway, I also pressed the AF On button. The camera switched to 3D without my needing to take my finger off the shutter release button. The focus area indicator in the EVF showed 3D and also there was a 3D box that followed my subject if I moved the camera around a bit. So think it was in 3D. Will have to try it outside later today.
Do you have your AF On button configured to switch the AF to 3D or to both switch the AF to 3D and initiate AF?
for a quickly moving subject, go from half press of a shutter to AFon while holding the shutter button halfway - the focus point transfers nicely.
if there not too much movement in the subject you can let go of the shutter release and engage the AF on for 3d tracking.
it just depends on whether the camera will lose focus if you let go of the wide area focus button while a subject moves quickly while handing over the focus point.
try this on a static subject and move the object in the frame by moving the camera.