Try this web page at techpout or the Apple forum page here.

1. Update Windows 10 to latest (just in case).

2. Download Apple Boot Camp Drivers (Download Boot Camp Support Software 5.1.5769). Thats the latest I could find.

3. Execute \bootcamp5.1.5769\BootCamp\Drivers\Apple\AppleWirelessMouse64.exe and done!

3.alt. Alternatively you can unpack AppleWirelessMouse64.exe and run DPInst.exe

I Found this solution on the thread check if this helps you,

1) If you've already added your Magic Mouse as a Bluetooth device in Windows 10, remove it before beginning.

2) Download Apple's Bootcamp Support Software from official website.

3) Unzip the file and navigate to the following folder:
bootcamp5.1.5769\Bootcamp\Drivers\Apple

4) Double-click on the file AppleWirelessMouseDriver64.exe. This will install the proper driver for the Magic Mouse.

5) Add your Magic Mouse under Windows 10 Bluetooth devices.

Regards,
J Wick