How to disable WiFi in Raspberry Pi4, possibly keeping the chip powered off.
Raspbian is managing hardware with overlays. In
/boot/overlays/README you will find:
Name: pi3-disable-wifi Info: Disable Pi3 onboard WiFi Load: dtoverlay=pi3-disable-wifi Params: <None>
I suggest you just add
/boot/config.txt to disable wifi. I have tested it with a Raspberry Pi 4B. It is also valid for Pi4. When disabled you will not get a WiFi interface wlan0 as you can check with
ip -br addr.
As @JeffAtwood noted in his comment it may also be possible to use
dtoverlay=disable-wifi but could not find an official source for this. @JeffAtwood don't tell us where he got the information, so just try it.
Create /etc/modprobe.d/brcm-blacklist.conf with the following content:
blacklist brcmfmac blacklist brcmutil
Reboot, and WiFi should be disabled. You may find errors in the system log depending on what method you are using to configure the network. You can choose to correct those, or not, of course.
rfkill block wifi and reboot to disable and
rfkill unblock wifi and reboot to enable it again.