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.

Answer from jksoegaard on Stack Exchange
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Apple
cdsassets.apple.com › live › 6GJYWVAV › user › ma1780_smart-keyboard-numeric-keypad-2017-ug.pdf pdf
English 1 Welcome to your Apple Magic Keyboard with Numeric Keypad
with Numeric Keypad · Your Apple Magic Keyboard has a · rechargeable battery and uses Bluetooth® · technology to connect wirelessly to · your Mac. This guide shows you how to use your · Magic Keyboard, including pairing, customization, and recharging the battery.
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Apple Support
support.apple.com › guide › iphone › pair-magic-keyboard-iph4288319c0 › ios
Pair Magic Keyboard with iPhone - Apple Support
Magic Keyboard connects to iPhone using Bluetooth®. Make sure the keyboard is turned on and charged. On iPhone, go to Settings > Bluetooth, then turn on Bluetooth. Select the device when it appears in the Other Devices list. Note: If Magic Keyboard is already paired ...
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Amazon
amazon.com › Apple-Magic-Keyboard-Numeric-Keypad › dp › B0DWTT6Z7H
Amazon.com: Apple Magic Keyboard with Numeric Keypad: Wireless, Bluetooth, Rechargeable. Works with Mac, iPad, or iPhone; US English - White : Electronics
... WIRELESS, RECHARGEABLE CONVENIENCE — Magic Keyboard with Numeric Keypad connects wirelessly to your Mac, iPad, or iPhone via Bluetooth. And the rechargeable internal battery means no loose batteries to replace.
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Apple
apple.com › all accessories › mice & keyboards › magic keyboard with numeric keypad - us english
Magic Keyboard with Numeric Keypad for Mac models - Apple
Magic Keyboard with Numeric Keypad - US English
The Magic Numeric Keyboard features a sleek new design and a rechargeable battery that powers it for a month between charges, and pairs automatically with your Mac.
Price   $129.00
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Magic Utilities
magicutilities.net › magic-keyboard › help › bluetooth-pairing
Magic Keyboard Bluetooth pairing - Magic Utilities
Enter a given numeric code on the Apple Wireless Keyboard and press return. Enter 1234 on an existing main keyboard (can be the on-screen keyboard) and click Allow (or press Enter), now enter 1234 on the Apple Wireless Keyboard and press return. In Windows 10, sometimes your device is paired, ...
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Apple Support
support.apple.com › en-us › 112037
Magic Keyboard with Numeric Keypad - Technical Specifications - Apple Support
The numeric keypad is also great for spreadsheets and finance applications. And the built-in, rechargeable battery is incredibly long-lasting, powering your keyboard for about a month or more between charges.1 ... Testing conducted by Apple in April 2017 using preproduction Magic Keyboard devices, firmware, and software with shipping iMac systems. Testing consisted of full battery discharge while engaging the device on a paired ...
Find elsewhere
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Apple
apple.com › all accessories › mice & keyboards › magic keyboard with touch id and numeric keypad for mac models with apple silicon (usb–c) - us english - black keys
Magic Keyboard with Touch ID and Numeric Keypad for Mac models with Apple silicon (USB-C) - US English - Black Keys - Apple
Magic Keyboard with Touch ID and Numeric Keypad for Mac models with Apple silicon (USB–C) - US English - Black Keys
Magic Keyboard with Touch ID and Numeric Keypad features a sleek design and a long lasting rechargeable battery and pairs automatically with your Mac. Buy now.
Price   $199.00
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Apple Support
support.apple.com › guide › mac-pro › magic-keyboard-touch-numeric-keypad-apde6983e835 › mac
Magic Keyboard with Touch ID and Numeric Keypad - Apple Support
You can use Magic Keyboard with Touch ID and Numeric Keypad anywhere within range of your computer. When you need to charge the keyboard, or if you need to pair it again, connect it to your Mac Pro using a USB-C Charge Cable.
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Manuals+
manuals.plus › asin › B0DWTT6Z7H
Apple Magic Keyboard with Numeric Keypad (Model MXCJ3LL/A) User Manual
Ensure the keyboard is charged and turned on. The power switch is located on the back edge of the keyboard. For initial pairing with a Mac, connect the keyboard to your Mac using the Lightning to USB Cable.
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Apple
support.apple.com › en-sg › guide › iphone › iph4288319c0 › ios
Pair Magic Keyboard with iPhone - Apple Support (SG)
Magic Keyboard connects to iPhone using Bluetooth®. Make sure the keyboard is turned on and charged. On iPhone, go to Settings > Bluetooth, then turn on Bluetooth. Select the device when it appears in the Other Devices list. Note: If Magic Keyboard is already paired ...
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Apple Community
discussions.apple.com › thread › 255487718
Using the Apple Magic Keyboard with numer… - Apple Community
Force Wired Mode on Magic Keyboard with Touch ID On Windows/Linux, the keyboard works fine via wire (no bluetooth connectivity required). On macOS, it will only connect over bluetooth (it will not work if bluetooth is disabled). Is there any way to force it to connect via wired connection? The bluetooth is laggy at times. Thanks! 3011 4 · How to force Bluetooth recognition of Magic Keyboard for pairing when there is no way to plug in a cable to a wireless keyboard Have replaced my old 2011 MacMini base unit with an M1 and hope to use existing mouse & Magic Keyboard.
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Apple Community
discussions.apple.com › thread › 254887970
turn on numeric pad on magic keyboard - Apple Community
If your keyboard has a separate keypad but no Num Lock key, try pressing Shift-Delete. If the numeric keypad still doesn’t work as you expect, you may have enabled Mouse Keys, which lets you move the pointer with the keypad. To turn Mouse Keys off, choose Apple menu > System Settings, click Accessibility in the sidebar, click Pointer Control on the right (you may need to scroll down), then turn Mouse Keys off. ... Magic Keyboard Numeric Keypad not working I just bought this keyboard and I can't figure out how to get the numeric keypad to work because it doesn't have a numbers lock button on it?
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Best Buy
bestbuy.com › best buy › computers & tablets › computer accessories & peripherals › mice, keyboards & accessories › computer keyboards › wireless & bluetooth keyboards › apple - magic keyboard full size with numeric keypad (lightning port) - silver/white
Apple - Magic Keyboard with Numeric Keypad - Silver
Apple - Magic Keyboard full size with Numeric Keypad (Lightning Port) - Silver/White
Magic Keyboard with Numeric Keypad features an extended layout, with document navigation controls for quick scrolling and full-size arrow keys for gaming. A scissor mechanism beneath each key allows for increased stability, while optimized key travel and a low profile provide a comfortable and precise typing experience. The numeric keypad is also great for spreadsheets and finance applications. And the built-in, rechargeable battery is incredibly long-lasting, powering your keyboard for about a month or more between charges.
(4.8)
Price   $129.99
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FIU Panther TECH
panthertech.fiu.edu › Apple-Magic-Keyboard-with-Touch-ID-and-Numeric-Keypad-for-Mac-models-with-Apple-silicon-US-English
Apple Magic Keyboard with Touch ID and Numeric Keypad for Mac models with Apple silicon - US English (USB-C)
Apple Magic Keyboard with Touch ID and Numeric Keypad for Mac models with Apple silicon - US English (USB-C)
OverviewMagic Keyboard is available with Touch ID, providing fast, easy, and secure authentication for logins and purchases.Magic Keyboard with Touch ID and Numeric Keypad delivers a remarkably comfortable and precise typing experience. It features an extended layout, with document navigation controls for quick scrolling and full-size arrow keys, which are great for gaming. The numeric keypad is also ideal for spreadsheets and finance applications. It’s wireless and features a rechargeable battery that will power your keyboard for about a month or more between charges.¹ It pairs automatically
Price   $179.00