alfa AWUS036AC USB WIFI adapter

Solution 1:

With a working temporary internet connection:

sudo apt-get install linux-headers-generic build-essential git
git clone https://github.com/abperiasamy/rtl8812AU_8821AU_linux.git
cd rtl8812AU_8821AU_linux
make
sudo make install
sudo modprobe rtl8812au

It 'makes' with a couple of possibly harmless warnings but no errors on my system.

After Update Manager installs a later kernel version, also known as linux-image, and after the required reboot, recompile:

cd ~/rtl8812AU_8821AU_linux
make clean
make
sudo make install
sudo modprobe rtl8812au

Please retain the file and these instructions for that time.