Plenty of sound advice above. Although perhaps there are too many options based on first comparisons of Nikon-Fit telephotos [overview appended bottom], they can be filtered into at least 4 categories.
Zoom Telephotos, Flexibility where a Zoom is better, and obviously much quicker than swopping a TC off or on. The 100-400 S is the most logical, although a 200-600 Z mount is roadmapped. The "Bigmas" are heavier but get you to 600mm. The 180-400 TC14 is one of my best all rounder wildlife lenses but limited to birds at sufficiently close distances. It also weighs 3.5kg
Lightest Primes, The 500 PF and 400 f4.5S win big time in the light weight category, especially for hiking and BIF. Both these remarkble telephotos pair very well with their TC14 on Z cameras.
Exotic Primes, The heavier E FL and Z (2 models have integral bespoke-TCs) include the succession of models of the 300 f2.8, 400 f2.8, 500 f4, 600 f4. These are all unmatched for quality and versatility, as each pairs very well with Teleconverters, but there's the factors of their weights and prices!
800mm (Plus), The 800 PF is very good; indeed it's unique in key respects. Its
image quality is very close to the legendary 800 f5.6E, but at significant savings in cost and weight. Small birds often demand at least 800mm to obtain decent FX framing, and 1000mm or 1120mm, 1600mm even, reach is often needed. This
schematic below illustrates these challenges, to achieve decent framing of smaller subjects, and/or at longer distances.
Using a DX crop in-camera on a 45mp sensor is often a useful tactic for birds, and the images work well on social media platforms.
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