GNU/Linux MX 19 Installing Broadcom BCM4321/BCM4322 Driver Guide
How to Install Broadcom BCM4321/BCM4322 Wi-fi/Bluetooth Driver on MX GNU/Linux 19.
The Package Provides the Source Code for the wl Kernel Modules and makes use of the DKMS Build Utility to Install them for the Running Kernel.

GNU/Linux MX Broadcom BCM4321/BCM4322 Driver Installation Guide