Was having a great day, everything was working as well as it could be. Suddenly. BANG! "No Wifi Adapter Found" on my Macbook running Ubuntu 20.04. After lots of googling, and trial & error. It worked. I'm writing this in hopes that it will help someone who was in my predicament.
Step 1 : Find an internet connection. I tethered my phone to macbook with a USB cord.
Step 2: Open your terminal and run the following :
sudo apt-get purge bcmwl-kernel-source
sudo apt-get install broadcom-sta-source broadcom-sta-dkms broadcom-sta-common
Then Reboot. Should work. It did for me. Good luck.