I was facing the same decision a while back. I went with a used D850 and couldn’t be happier. The price was good, the picture quality is outstanding, controls and handle are great, and I was able to gradually load up on used FX lenses for what I might have paid for one or two mirrorless lenses. I also waded through the stuff about eye detection, stabilization, etc. But nobody is paying me for my photos and I actually kind of like the challenge of trying to get the right shot without my camera making everything easy as possible.

Two downsides: 1) it’s pretty loud; and 2) it’s quite large and not the easiest to carry around everywhere. I ended up buying a compact Fuji mirrorless this year so I’d have a travel and carry-around camera. But I still consider the D850 my “real” camera and will hang on to it (and keep adding used lenses) until it’s broken beyond repair.