Ubuntu 18.04 Application menu not showing after clicking

You have to activate "hot corners" with gnome-tweak-tools.

It worked for me.

I found this solution here : https://extensions.gnome.org/extension/6/applications-menu/

cd /usr/share/gnome-shell/extensions/[email protected]

Then edit metadata.json

sudo nano metadata.json

Edit the Shell Version

{
"extension-id": "apps-menu",
"uuid": "[email protected]",
"gettext-domain": "gnome-shell-extensions",
"name": "Applications Menu",
"description": "Add a category-based menu for applications.\nThis extension is part of Classic Mode and is officially supported by GNOME. Please do not report bugs using the form below, use GNOME's GitLab instance instead.",
"original-authors": [ "[email protected]", "[email protected]" ],
"shell-version": [ "3.28.1" ], // add your shell version
"url": "https://gitlab.gnome.org/GNOME/gnome-shell-extensions"
}

Press ctrl+o to save the file and ctrl+x to exit

Get Shell Version by typing : gnome-shell --version

Then Logout and Login again, This fixed my issue.