I have an old 2014 11-inch MacBook Air that I decided to dig out to give (Omarchy)[https://omarchy.org] a spin. Unfortunately the broadcom wifi adapter wasn’t recognized either during installation nor after. Here are the incantations that allowed the adapter to be seen and configured.

During Installation

modprobe -r b43
modprobe -r bcma
modprobe wl

From here you can go into iwctl and connect to your wifi network. See instructions.

After Installation

Download the broadcom-wl, broadcom-wl-dkim, and dkim (see list of dependencies in broadcom-wl-dkim) packages from https://archlinux.org/packages/?sort=&q=broadcom-wl (click on the tiny “Download from Mirror” link in the upper right) on to a USB drive from a computer with internet access.

Get those packages onto your archlinux computer by plugging the USB drive into it:

fdisk -l # See the name of the USB drive
sudo mkdir /mnt/usbdrive
sudo mount /dev/<NAME OF USB DRIVE - Ex: sdb1> /mnt/usbdrive
cp /mnt/usbdrive/broadcom-wl-6.30.223.271-636-x86_64.pkg.tar.zst .
cp /mnt/usbdrive/broadcom-wl-dkms-6.30.223.271-44-x86_64.pkg.tar.zst .
cp /mnt/usbdrive/dkms-3.2.1-1-any.pkg.tar.zst .
sudo umount /mnt/usbdrive # Unmount

sudo pacman -U broadcom-wl-6.30.223.271-636-x86_64.pkg.tar.zst
sudo modprobe wl

If that doesn’t work, install the dkms packages and try again.

From here you can go into iwctl and connect to your wifi network. See instructions.