How to turn off screen rotation in Ubuntu 18.04 LTS?

The best solution I have found so far is to use the icon that is available in the top right corner of the screen, when you click on the down arrow. The icon is the one in red in the screenshot below:

It might also look like this:

If you want to remove this feature then fire below commands :

Try this command to stop and disable

$ sudo systemctl stop iio-sensor-proxy.service
$ sudo systemctl disable iio-sensor-proxy.service

Try this command to remove

$ sudo apt-get remove iio-sensor-proxy

gsettings set org.gnome.settings-daemon.plugins.orientation active false

The above just worked for me. Seems the simplest solution