Wireless internet missing. No icon or settings

Checking the issue with these two commands to find out what Wi-Fi adapter you are using and do you have any information about missing firmware.

sudo lspci
sudo update-initramfs -u

Getting Internet

We need a temporary internet connection to fix WiFi. Ways to connect :

Connect USB cable and use USB Tethering in your phone to connect your computer to the internet (through phone's cellular data/WiFi)Use wired ethernet cable for connecting to internet.

Prerequisite

You should install the corresponding header of your kernel. Open terminal and type:

This as first:

sudo apt-get install linux-headers-`uname -r` 

Next, install the packages necessary for building :

This as second:

sudo apt-get install git build-essential dkms

Then type in terminal as third:

cd 

And then type this as fourth command in order, everything in one line.

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

Type this as fifth command:

sudo dkms add rtlwifi_new 

Type this as sixth command:

sudo dkms install rtlwifi-new/0.6

Restart laptop.

If you will have issue with typing commands one by one, use this one-liner:

sudo apt-get install linux-headers-`uname -r` && sudo apt-get install git build-essential dkms && cd  && git clone -b extended --single-branch https://github.com/lwfinger/rtlwifi_new.git && sudo dkms add rtlwifi_new  && sudo dkms install rtlwifi-new/0.6

And then restart laptop.

Other methods described here:

https://subinsb.com/install-realtek-d723-wifi-driver-linux/