Wifi on Old Mac with Ubuntu

Check Wifi adapter

sudo lshw -class network

Broadcom Adapter BCM4360

       description: Wireless interface
       product: BCM4360 802.11ac Wireless Network Adapter
       vendor: Broadcom Inc. and subsidiaries

Install packages

sudo apt update
sudo apt install broadcom-sta-common broadcom-sta-dkms

Reboot, and Wifi is working.