Please remember that Broadcom considers its drivers proprietary. Distributors are not permitted to include Broadcom drivers as default. End users, however, are permitted to download/Install Broadcom drivers for free.
The easiest method is by connecting using another means, for example mobile phone using Hotspot connected using USB tether. Then run in terminal:
sudo apt update && sudo apt install firmware-b43-installer b43-fwcutter bcmwl-kernel-source