Step 1 - Installing WiFi firmware files

Follow the generic instructions on the wifi guide until (including) point 3. in the On Linux section.

Step 2 - Installing IWD

sudo pacman -S iwd wifi-fix-mbp
systemctl stop wpa_supplicant
systemctl mask wpa_supplicant
sudo nano /etc/NetworkManager/NetworkManager.conf

paste in this at the end:

[device]
wifi.backend=iwd

Run:

systemctl enable iwd
systemctl enable wifi-fix.service

then reboot.