In short, the driver on Github has problems. If you installed the driver from GitHub (https://github.com/aircrack-ng/rtl881..., it simply does not work for now. I hope the developers can fix the problem soon. The problems seem to exist for many months.
Use the following command to install the driver:
sudo apt install realtek-rtl88xxau-dkms
More detailed steps on setting up Kali Linux for penetration test can be found here:
https://github.com/legendPerceptor/et...