Wifi is not working on Linux Mint 19.

sudo apt-get install dkms git build-essential 

git clone -b extended https://github.com/lwfinger/rtlwifi_new.git 

sudo dkms add ./rtlwifi_new 

sudo dkms install rtlwifi-new/0.6 

sudo cp -r rtlwifi_new/firmware/rtlwifi/ /lib/firmware/rtlwifi 

echo "options rtl8723de ant_sel=2" | sudo tee /etc/modprobe.d/rtl8723de.conf(references)