How do you connect an Apple Magic Keyboard with Numeric pad to Windows 10 via Bluetooth?
When you have the Windows Bluetooth pane open and it is searching for devices then slide the power control on the keyboard to Off and then On shortly after. This should make the keyboard discoverable by Windows.

Make sure that the keyboard is not plugged in via cable to another computer, and make sure that it is not able to communicate with a previously paired Mac at the same time.

Note that the comments you have received earlier regarding duplicates and directions concerns a completely different keyboard, namely the "Apple Wireless Keyboard". You have the "Apple Magic Keyboard" which works in a slightly different manner regarding Bluetooth pairing - and it doesn't have a power button, but rather a slider.