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
🌐
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 with another device, you ...
🌐
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.
🌐
Manuals+
manuals.plus › asin › B0DWTT6Z7H
Apple Magic Keyboard with Numeric Keypad (Model MXCJ3LL/A) User Manual
This wireless, Bluetooth-enabled keyboard is designed for use with compatible Mac, iPad, and iPhone devices, offering a comfortable and precise typing experience with an extended layout and numeric keypad. Image: Angled view of the Apple Magic Keyboard with Numeric Keypad, showcasing its slim profile and full key layout. Verify that your package contains the following items: ... Image: Lightning to USB Cable. This cable is used for charging the keyboard and for initial pairing with a Mac.
🌐
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.
Find elsewhere
🌐
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
🌐
Apple Community
discussions.apple.com › thread › 250145562
"Wired mode" for Magic Keyboard with Numeric Keypad
I understand that the Magic Keyboard with Numeric Keypad is wireless and that it can be recharged with the included lightning cable in the box.
🌐
Apple
support.apple.com › en-gb › guide › iphone › iph4288319c0 › ios
Pair Magic Keyboard with iPhone – Apple Support (UK)
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 ...
🌐
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 ...
🌐
Best Buy
bestbuy.com › best buy › computers & tablets › computer accessories & peripherals › mice, keyboards & accessories › wireless & bluetooth keyboards
Apple Magic Keyboard full size with Numeric Keypad (Lightning Port) Silver/White MXCJ3LL/A / MQ052LL/A - Best Buy
Shop Apple Magic Keyboard full size with Numeric Keypad (Lightning Port) Silver/White products at Best Buy. Find low everyday prices and buy online for delivery or in-store pick-up. Price Match Guarantee.
🌐
RTINGS
rtings.com › home › keyboard › reviews › magic keyboard with touch id and numeric keypad
Apple Magic Keyboard with Touch ID and Numeric Keypad Review - RTINGS.com
October 6, 2021 - The Apple Magic Keyboard with Touch ID and Numeric Keypad is the second generation of the Apple Magic keyboards, replacing the Apple Magic Keyboard 2017. There a...
🌐
Amazon
amazon.com › Apple-Wireless-Keyboard-Numeric-Keypad › dp › B07JMZH19Y
Amazon.com: Apple Magic Wireless Keyboard with Numeric Keypad - US English (Renewed) : Electronics
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.