Disabling the WiFi Module on Raspberry Pi

1. Modify your /boot/config.txt file inside your Raspberry Pi's SD card.
2. Add a line dtoverlay=disable-wifi to the file and save changes.
3. Reboot the Raspberry Pi.

NOTE

If you wish to have WiFi module re-enabled for another purpose, you can repeat the steps above but ignore step 2 and comment out the dtoverlay=disable-wifi

Source: https://forums.raspberrypi.com/viewtopic.php?t=342095#p2049384