Installing driver for TP-LINK Archer T9UH AC1900 on Ubuntu 18.04
Solution 1:
With a temporary working internet connection by ethernet, tethering or whatever means possible, open a terminal and do:
git clone https://github.com/zebulon2/rtl8814au.git
sudo dkms add ./rtl8814au
sudo dkms install rtl8814au/4.3.21
Reboot. Your wireless should now be working.