I recently decided to dual boot linux my macbook air from 2014 (or maybe 2015). Apparently dual booting on macOS works really well, since you will enter GRUB on normal boots, but can enter macOS by holding the alt/option key during boot. However, there are no free wifi drivers available, so you will need to download extra non-free drivers, which can be really annoying if you only have wifi to connect by, and wifi doesn’t work.
Since apt doesn’t work without WiFi. I mounted the USB-stick with the installation media and copied it all to /opt/apt. Then I rebooted into macOS and flashed the usb-stick with normal FAT so I could use it as plain storage. My wifi hardware is 03:00.0 Network controller: Broadcom Limited BCM4360 802.11ac Wireless Network Adapter (rev 03), and getting it to work is actually pretty well explained on the Debian wiki wl page. Pop over to the debian packages-page and download broadcom-sta-dkms and any dependencies you might need. If you miss any now you will need to reboot to macOS later and fetch them. Copy all the packages to the USB-stick.
Reboot into linux. Copy the packages into the correct folder under /opt/apt/. Point out in apt that you want to use /opt/apt/ as a repository (file:/opt/apt in /etc/apt/sources.list and disable security). Run sudo apt-get install linux-image-$(uname -r|sed 's,[^-]*-[^-]*-,,') linux-headers-$(uname -r|sed 's,[^-]*-[^-]*-,,') broadcom-sta-dkms. When completed, try to remove all other conflicting kernel modules by running modprobe -r b44 b43 b43legacy ssb brcmsmac bcma and the modprobe wl. I needed to reboot after this to get the wifi interface up and running.
In my case, I lost the kernel module as soon as I updated to a new kernel version, despite the dkms installed. Maybe this is how it works when you install from your crappy self-hosted apt repo? Anyways, I reinstalled the broadcom-sta-dkms so hopefully it will automatically build in the future.
Still. Don’t think the wl driver will work well. Especially going to sleep and back seems to mess up the driver. Sometimes you may need to reboot the computer to get it up and working again. But to the honest, I have that same problem when running macOS as well. That’s all I have to say about that.