After installing the
gnome-tweak extension my left Super key did not work anymore (to raise the activities window).
To try and fix the problem I uninstalled the the tweak tool with
sudo apt-get remove gnome-tweak-tool, but that did not fix the problem. I then mistakenly uninstalled all the extensions using
sudo apt-get purge gnome-shell-*. My bad.
Upon restart I was greeted with a terminal window, no login screen. Thus I had to install the gdm3 extension,
supo apt-get install gdm3, to get a login screen and desktop. Now the menu bar on the left is still missing.
To avoid a reinstall/repair I would simply like to install all the default extensions which come with the ubuntu 18.04 LTS package. Where can I find the list of all these default extensions? I have searched far and wide and could not find it (not even on the help website).
EDIT: There was an answer provided, but quickly deleted, suggesting I install the gnome desktop again -
sudo apt-get install ubuntu-gnome-desktop. After doing so everything seems to be back to normal. I am not sure if all the default extensions are installed though.