Just catching up on this thread... I went through this last year. I was basically in the same boat when I got my D850 and realized my old lenses just werent cutting it anymore. That sensor is honestly SO demanding and shows every little flaw! I spent weeks comparing options because I wanted that perfect mix of macro and portraits. I looked at the Venus Laowa 100mm f/2.8 2X Ultra Macro APO first. Its actually wild because it goes to 2:1 magnification, which is awesome for dew drops and tiny insects. The sharpness is incredible, but be careful because it's manual focus only. For portraits, that can be a real struggle if your subject moves even a tiny bit, especially with the thin depth of field on a D850. Then I checked out the Tokina atx-i 100mm f/2.8 FF Macro. It's a bit of a hidden gem imo. The glass is super sharp and the colors are really nice for skin tones, but the autofocus is definitely "old school" and makes a bit of noise. Also, it doesn't have image stabilization, which might be a dealbreaker if you shoot handheld nature shots a lot. If you have the budget, you might want to consider the Zeiss Milvus 100mm f/2 Makro-Planar. I tried one out and the bokeh is just... wow. It’s like butter. But yeah, it's super heavy and very pricey, so idk if it's worth it for everyone. Honestly, it's a tough choice cuz you're balancing speed, stabilization, and sharpness. I'm still learning the ropes myself, but I've found that for the D850, you really cant compromise on the glass quality or you'll see it in the final crop lol. Hope my rambling helps a bit! Cheers.

In my experience, the D850 is a beast that shows every flaw in ur glass, so u gotta be picky. I've been shooting with that sensor for years and honestly, the Tamron SP 90mm f/2.8 Di Macro 1:1 VC USD (Model F017) is the winner for me. It's ridiculously sharp—like, scary sharp—and the bokeh is way smoother than the Nikon version imo. Ngl, the Nikon AF-S VR Micro-Nikkor 105mm f/2.8G IF-ED is a classic and the AF is snappy, but it feels a bit "clinical" for portraits. If u want creamy backgrounds for headshots plus insane detail for bugs, the Tamron is sooo good. - Tamron SP 90mm f/2.8 Di Macro 1:1 VC USD (Model F017): Best rendering and bokeh for portraits.
- Nikon AF-S VR Micro-Nikkor 105mm f/2.8G IF-ED: Snappiest AF for moving insects.
- Sigma 105mm f/2.8 EX DG OS HSM Macro: Great budget-friendly sharpness. Basically cant go wrong with the Tamron tho. gl!

Like someone mentioned, that D850 sensor is basically a microscope and shows every little flaw in your glass. If ur trying to be cost-conscious but still want professional results, you should look at the Tokina atx-i 100mm f/2.8 FF Macro. It's significantly cheaper than the Nikon glass but surprisingly sharp even on those 45 megapixels. Just a quick tip tho: it uses a push-pull clutch for focus which is kinda old-school, so dont expect it to hunt down fast-moving bugs like a pro sports lens. Also, with high-res sensors, even tiny vibrations will ruin a macro shot, so definitely try to use a tripod whenever possible. It works great for portraits too since the rendering is a bit more characterful and less clinical than some of the newer stuff.