In my experience, the D500 does work better in low light AF, especially for macro. It can basically see in the dark...The IQ is better on the D850 for sure; bigger sensor as well as low light wide angle shots.
Here's a D500 album for Lembeh.
D500 Lembeh Straits
Here's a D500 album for Lembeh.
D500 Lembeh Straits