Mac Mini Wireless Not Working Correctly After Installing Linux Mint

If you find that your Mac Mini's wireless card is not working correctly after installing Linux Mint (mine was not displaying available wireless networks) try these steps:

first make you you've got the right driver (my Mac Mini needs the Broadcom BCM4321 802.11a/b/g/n driver):

sudo apt update
sudo apt install firmware-b43-installer
sudo reboot

If that doesn't resolve the problem try switching drivers (in my case the wl driver seems to be the problem):

sudo modprobe -r wl
sudo modprobe b43

Check to see if wireless networks are displayed, if so then add the wl driver to the blacklist:

sudo touch /etc/modprobe.d/blacklist.conf
sudo echo "blacklist wl" >> /etc/modprobe.d/blacklist.conf

The b43 should then become the default driver.
You may need to manually edit the blacklist file with elevated privileges
eg: 

# blacklist wl driver as it wont list available wireless networks
#https://www.linuxquestions.org/questions/linux-networking-3/ubuntu-16-04-mac-mini-2009-broadcom-driver-selected-and-wlan-enabled-but-home-network-does-not-show-4175600634/
blacklist wl 

See original article here.