TIP: Turn on D850 eye/face detection AF (Auto Focus)         Even if Nikon hasn't officially introduced human/animal eye/face/head detection AF (Auto Focus) on any of their DSLRs, you can do this by tweaking the D850 settings, to mimic at some extent the firmware upgrades they have released for the Z line.
That's because, unlike modern MILC (mirrorless) cameras, the D850 [or any Nikon DSLR for that matter] doesn't have 5 axis movement/vibration stabilization built into the camera/lenses, and on top of that the PDAF (Phase Detection Auto Focus) option is sketchy at best in most situations, and especially with subjects moving at high speeds.
The obvious alternative would be to use Manual [M] mode, which is way too slow, therefore that's not an option in the wild with fast flying birds/airplanes, running animals/people, or speeding vehicles.
But the D850 has an advantage: it performs better with 3D tracking AF turned on than some of the mirrorless out there.
In order to enable D850 eye/face AF all these settings need to be enabled/selected/turned on ➜ [Custom Settings: Fine-Tuning Camera Settings]:

• [a1] = AF-C Priority Selection = Focus
• [a2] = AF-S Priority Selection = Focus
• [a3] = Focus (AF) Tracking with Lock-On:
  • Blocked shot AF response = Quick [Q] ➜ fastest response with minimum delay
  • Subject motion = Erratic [E] ➜ hardest/slowest tracking covers entire area
• [a4] = 3D-Tracking (AF) Face-Detection = ON
• [a5] = 3D-Tracking (AF) Watch Area = Wide
• [a8] = AF Activation = Shutter/AF-ON
• [a10] = Autofocus (AF) Mode Restrictions = No restrictions
• [a12] = Focus Point Options:
  • Focus point illumination = ON
  • Manual focus mode = ON
  • Dynamic-area AF assist = ON
• [a13] = Manual Focus Ring in AF Mode = Enable

Also, make sure you take all your photos using the OVF (Optical ViewFinder).