Ubuntu 18.04 Gnome must have

The pre-installed GNOME Calculator in Ubuntu 18.04 is a snap application which may lack some features provided by the traditional one due to restrictions of snap packages.

Remove the snap application by running

snap remove gnome-calculator
and install the traditional apt one by running

sudo apt install gnome-calculator
You may need to to restart GNOME shell by hitting Alt+F2, then typing r and pressing Enter for it to take effect.

https://extensions.gnome.org/extension/258/notifications-alert-on-user-menu/
https://extensions.gnome.org/extension/708/panel-osd/
https://extensions.gnome.org/extension/744/hide-activities-button/
https://extensions.gnome.org/extension/750/openweather/
https://extensions.gnome.org/extension/905/refresh-wifi-connections/
https://extensions.gnome.org/extension/800/remove-dropdown-arrows/
https://extensions.gnome.org/extension/355/status-area-horizontal-spacing/
https://extensions.gnome.org/extension/234/steal-my-focus/
https://extensions.gnome.org/extension/427/workspaces-to-dock/
https://extensions.gnome.org/extension/885/dynamic-top-bar/
https://extensions.gnome.org/extension/53/pomodoro/
https://extensions.gnome.org/extension/690/easyscreencast/
https://extensions.gnome.org/extension/97/coverflow-alt-tab/