In the Ubuntu 20.04 Gnome Shell, there is more space between the icons of the application indicators on the top panel. You can use an extension called Unite to reduce the spacing between icons.
Unite is a Gnome Shell extension that makes some layout tweaks to the top panel and removes window decorations to make it look like the Ubuntu Unity Shell. With extensions, the system tray area looks like this:
To install the extension, do the following steps one at a time:
1.) Open Terminal (Ctrl + Alt + T) and run the command:
sudo apt install chrome-gnome-shell
2.) Run the command to install the required extensions
sudo apt install x11-utils
3.) go to extensions.gnome.org/…/unite/Switch on, install extension.
If you don’t see the toggle icon, click the link to install the browser extension and refresh this web page
The extension narrows the spacing between items in the top bar by default. To tweak the appearance of other panels, open Gnome Tweaks (or an extension tool) and go to Unified Settings.