I remember in Ubuntu version we have one netspeed package which was capable to display real-time Download/Upload speed of interfaces. But in Ubuntu 20.04, this is fairly easy method to display Download/Upload speed of Ubuntu Desktop. We are considering for those Ubuntu 20.04 users who are using Gnome Desktop environment.
Actually gnome make these small packages included through Gnome-extension like Google Chrome extension. We just need to add these extension in our Desktop environment and it will start working.

Install NetSpeed gnome extension

For installation of netspeed extension, you have to open its extension page on web-browser and enable it.
Gnome netspeed extension page Clink to open it.
It might possible that this is your first extension through this browser, it might show you below page. you need to click on red highlighted to install browser extension.

Now refresh this page again,this time you will get to enable button on make it enable.

Once you install browser extension, you will get it appear on right and upper side like below.