Day 2 on Ubuntu. Wifi is gone. Apparently a well-known issue on Mac.

Error message when trying to fix:

Errors were encountered while processing:
 bcmwl-kernel-source
E: Sub-process /usr/bin/dpkg returned an error code (1)

Tried a lot of options. In the end this one worked. Whereas question refers to Ubuntu 16.04 the answer mentions Ubuntu 20.04 explicitly.