But perhaps there is a better solution. Take a look to this post:
I followed the @C0d3man’s recipe in my RBPI 3B+ Zynthian:
wget https://archive.raspberrypi.org/debian/pool/main/f/firmware-nonfree/firmware-brcm80211_20161130-3+rpt3_all.deb
sudo dpkg -i firmware-brcm80211_20161130-3+rpt3_all.deb
And uncommented the lines again. It works too, and now the internal WIFI device is working again.
Regards,