The hot corner where when the mouse is over on top left corner of the screen activates the Activities (same effect as Windows Key or clicking on Activities at the top) is very annoying.
Suggestions to edit some /usr/share/gnome-shell/js/ui/layout.js file did not do the trick. However, the quick and easy fix is Activities Configurator. The extension provides quick fix. A window popup (or a smiley face appears next to the Activities button) after activating the extension and there are many things to configure including "disable hot corner".