This is a cut and paste from the link I posted above.
This driver works pretty well, however it doesn't support 5GHz networks and during my usage I found it would drop the connection intermittently.
To install the b43 driver, run the following command in a terminal
apt install firmware-b43-installer
and rebooting eOS
This is ...
I had a similar issue on a MacBook Air and used the instructions on AsK Ubuntu
sudo apt update
sudo apt install firmware-b43-installer
sudo apt install linux-firmware
The kernal drivers should now show in App Center.