You can download the Webmin PGP key with wget and add it to your system's list of keys:
$ wget -q -O- http://www.webmin.com/jcameron-key.asc | sudo apt-key add.
Next, update the list of packages again in order to include the now-trusted Webmin #repository:
$ sudo apt update.
Here, you will learn how to install the #Webmin control panel on an Ubuntu 18.04 or #Ubuntu 20.04 server.
https://linuxapt.com/blog/37-how-to-install-webmin-on-ubuntu-20-04-lts
