Historically - the pre Z9 era - Auto AF mode has worked very well for wildlife subjects, but under restricted conditions. Otherwise, the focus can be relied upon to grab what ever is in front of the subject (or the background, especially on small subjects in the frame). This has been the case since it was introduced in the DSLRs (AutoAF mode has been around since the D3, circa 2007). For example, with the D850, D5, D500, AutoAF often works very well for BIF in open skies, or in some sports scenes.
It finally dawned on me that all the Nikon Group AF modes operate as corralled versions of AutoAF. These modes all use Closest Focus Priority (CFP). However with the Z9, active Subject Recognition overrides the CFP algorithm, which often grabs the subject reliably in the case of AutoAF. This unless S-R is discombobulated by a tricky subject and/or too much vegetation or other clutter. As discussed and shown, the updates improving the Deep-Learning in the Z9 SR have reduced this complication.
In summary, to return to the Z9 (and Z8) one has the power to put to work a hierarchy of AF modes that combine the best of CFP and SR. Using a set of 3 or even more of these modes, you can corral the search area across - or within - the scene to grab tricky subjects. There's the choice between the trio of AutoAF > Wide > Small, or / with added flexibility: AutoAF, C1 and C2 customizable from 19*11 > 1*1.
also see dicusssion of these modes & challenges in Steve's
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