If there is one camera I regret letting go of, that is the D500. If there's a lens I regret parting ways with, it's the 500PF. If there's a combo I lament not keeping, it's the D500 + 500mm PF.
Don't get me wrong, the Z9 is a marvel. But if I am coldly objective, it has not allowed me to take pictures I could not take before with a D500 (or D850). But it has made things a lot easier and with many options to achieve what I want.
The D500 is built like a little tank. Because it was marketed as a wildlife/action camera, where it shines, sometimes it goes unsaid/unknown that it is very versatile camera. Pair it with Sigma's f/1.8 APSC zooms and you'll be have a surprisingly nice portrait camera (especially with the 50-100mm).
The 500 PF has nothing to envy from the new Z telephotos. Certainly not optically, though you'd have more stabilization with the newer lenses on Z bodies. Then again, if you are shooting BIF, for example, you'd be at shutter speeds at which you'd disengage VR.
Given your stated budget, a D500 + 500 PF would be a great option. Together they'll take great photos for 10 years, at least. If you want to go mirrorless in Nikon, the Z50ii has essentially the AF of the Z9. But shutter speed tops out at 1/4000.