- Save disable-cortana.reg as UTF-16 little endian with BOM or UCS-2 little endian with BOM
- Windows' Notepad calls that "Unicode"
- Double-click it and confirm any prompts
- Reboot Windows
To verify that it worked, open the start menu and type anything. Search should be limited to local results only and not blast all your keystrokes into the net.
Source: https://pureinfotech.com/disable-web-search-windows-10-version-1803/