Bought Nikon D850 but I can't read raw files in my CS6 photoshop

You need to download the free dng comverter.

Digital Negative (DNG), Adobe DNG Converter | Adobe Photoshop CC

Camera raw support is camera model specific. Support for new cameras is added to ACR as new versions are released, for the D850 this is ACR 9.12 (nine-twelve).

The latest ACR release that works on CS6 (which is now six major Photoshop versions behind!) is ACR 9.1.

You have bought a $3500 camera body, so $10 a month for an always up to date and current Photoshop seems reasonable, right? That's about fifteen years before you reach half the cost of the camera...