The upper left corner of the "active" button to display all open application windows, with a search box at the top, right side of the work area. Some users find it useless, and want to remove the button. And can be extended easily done by Gnome Shell.
1. Open the Ubuntu software, search for and install "Hide Activities Button" button.
Install the first. So far, it supports Gnome v3.34 or later (provided in Ubuntu 19.10 in).
2. To manage extensions, install and start Gnome Tweaks by Ubuntu software, and then go to the "Extensions" tab.
