18.04dockgnome-shellubuntu-dock
Although I have set "Auto-hide the Dock" to On, the dock does not disappear. The icons on the desktop move a bit to the left so that they are partly covered by the dock, but the dock remains there as long as there is no maximized window covering it.
The first picture shows an extract of my desktop with auto-hide on, the second with auto-hide off.
The third picture shows what I wanted and what I got through @pomsky's answer.
You may use a GNOME shell extension called "Hide Dash X" to achieve your goal.
Other alternative extensions:
Simply removing gnome-shell-extension-ubuntu-dock would not get rid of the GNOME dash. The dash is a default feature of GNOME shell. It only in appears Activities overview or Applications overview ("Show Applications" screen).
The gnome-shell-extension-ubuntu-dock package is an Ubuntu-only modification (a fork of the Dash to Dock extension), which converts the dash into a customisable dock. The dock appears anywhere, not just in Activities or Applications overview, and also has some other extra features.
So removing the package would only remove the dock-like feature, but the dash will stay as it is since it's an inbuilt feature of GNOME shell.
The current answer is you can't. This is a known bug since 17.10, https://bugs.launchpad.net/ubuntu/+source/gnome-shell-extension-ubuntu-dock/+bug/1723117
So didn't really fall thru the cracks, there isn't atm anyone assigned to fix as the most important thing about the Desktop version of Ubuntu currently is to limit the amount of resources used on it. (i.e money
Best Answer
That is the default behaviour. Ubuntu dock uses "intellihide" mechanism (i.e. dodges windows only) when it is set to auto-hide.
If you wish to keep it hidden until mouse-hover, open Terminal and run the following