Method 1 (worked)

To disable the top-left corner and prevent open Activities Overview, Go to this settings:

1. Open the settings
2. Type multitasking and open it
3. In General, toggle off Hot Corner

Method 2

You can also use command line:

gsettings set org.gnome.desktop.interface enable-hot-corners false

# check
gsettings get org.gnome.desktop.interface enable-hot-corners