How do I install drivers for Realtek RTL8812BU?

Almost all of the instructions are in the README on the second site you linked. I’ll fill in a few blanks.

With a working internet connection by ethernet, tethering or whatever means possible, open a terminal and do:

sudo apt-get update
sudo apt-get install build-essential dkms git
git clone https://github.com/cilynx/rtl88x2BU_WiFi_linux_v5.2.4.4_26334.20180126_COEX20171012-5044.git

Now, from the README:

cd rtl88x2BU_WiFi_linux_v5.2.4.4_25643.20171212_COEX20171012-5044
VER=$(cat ./version)
sudo rsync -rvhP ./ /usr/src/rtl88x2bu-${VER}
sudo dkms add -m rtl88x2bu -v ${VER}
sudo dkms build -m rtl88x2bu -v ${VER}
sudo dkms install -m rtl88x2bu -v ${VER}
sudo modprobe 88x2bu

Please be aware that the ‘build’ process takes a few moments; please be patient.

Your wireless should now be working.

You could try the next:

sudo apt-get update
sudo apt-get install build-essential dkms git
git clone https://github.com/cilynx/rtl88x2BU_WiFi_linux_v5.3.1_27678.20180430_COEX20180427-5959
cd rtl88x2BU_WiFi_linux_v5.3.1_27678.20180430_COEX20180427-5959
VER=$(sed -n 's/\PACKAGE_VERSION="\(.*\)"/\1/p' dkms.conf)
sudo rsync -rvhP ./ /usr/src/rtl88x2bu-${VER}
sudo dkms add -m rtl88x2bu -v ${VER}
sudo dkms build -m rtl88x2bu -v ${VER}
sudo dkms install -m rtl88x2bu -v ${VER}
sudo modprobe 88x2bu