Install gnome-tweak-tool

First, we need to enable universe repository. To do this, open Software and Update via application menu. Mark all universe repositories from the repo list.

Click Reload to update Ubuntu. Next, use the following command to install Gnome Tweak Tool

 sudo apt install gnome-tweak-tool

Output:

$ sudo apt install gnome-tweak-tool
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following NEW packages will be installed:
 gnome-tweak-tool
0 upgraded, 1 newly installed, 0 to remove and 435 not upgraded.
Need to get 205 kB of archives.
After this operation, 1,198 kB of additional disk space will be used.
Get:1 http://archive.ubuntu.com/ubuntu artful/universe amd64 gnome-tweak-tool all 3.26.2.1-1ubuntu1 [205 kB]
Fetched 205 kB in 1s (106 kB/s)            
Selecting previously unselected package gnome-tweak-tool.
(Reading database ... 145771 files and directories currently installed.)
Preparing to unpack .../gnome-tweak-tool_3.26.2.1-1ubuntu1_all.deb ...
Unpacking gnome-tweak-tool (3.26.2.1-1ubuntu1) ...
Processing triggers for mime-support (3.60ubuntu1) ...
Processing triggers for desktop-file-utils (0.23-1ubuntu3) ...
Setting up gnome-tweak-tool (3.26.2.1-1ubuntu1) ...
Processing triggers for gnome-menus (3.13.3-6ubuntu5) ...
Processing triggers for hicolor-icon-theme (0.17-1) ...

Now run Gnome Tweak Tool

Could be solved with a single command if you are facing this issue just after fresh install

1. Press CTRL + ALT + T
2. Type this command and enter your password.

sudo apt update && sudo apt upgrade && sudo apt-get install gnome-tweak-tool