Boot Camp 6.1.7866 is a specific version of the Windows Support Software

Error 1: “Boot Camp x64 is unsupported on this computer model.”

Cause: You are trying to install the 64-bit driver package on a 32-bit version of Windows (unlikely with Windows 10) or your Mac model is too new/too old.
Fix: Ensure your Mac is from the 2013–2018 era. For newer Macs (2019+), you need Boot Camp 6.1.8xxx or later.

certutil -hashfile Setup.exe MD5   (on Windows)
md5 Setup.exe                      (on Mac)

Disclaimer: This article is for informational purposes only. Apple, Boot Camp, macOS, and Windows are trademarks of their respective owners. Always back up your data before modifying Boot Camp drivers or partitions.

Open Boot Camp Assistant (found in /Applications/Utilities/).