Webmin and signatures couldn’t be verified because the public key is not available NO_PUBKEY 2D223B918916F2A2

You may get the following error while trying to update apt packages, where Webmin is one of them.

W: GPG error: https://download.webmin.com/download/newkey/repository stable Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 2D223B918916F2A2
E: The repository 'https://download.webmin.com/download/newkey/repository stable Release' is not signed.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.

Solution

This issue can be resolved in the following ways (execute lines in sudo mode):

Step 1

wget https://raw.githubusercontent.com/webmin/webmin/master/setup-repos.sh

Output:

--2023-10-13 07:56:54--  https://raw.githubusercontent.com/webmin/webmin/master/setup-repos.sh
Resolving raw.githubusercontent.com (raw.githubusercontent.com)... 185.199.111.133, 185.199.108.133, 185.199.109.133, ...
Connecting to raw.githubusercontent.com (raw.githubusercontent.com)|185.199.111.133|:443... connected.
HTTP request sent, awaiting response... 200 OK
Length: 5268 (5.1K) [text/plain]
Saving to: ‘setup-repos.sh’

setup-repos.sh                                          100%[=============================================================================================================================>]   5.14K  --.-KB/s    in 0s      

2023-10-13 07:56:54 (66.1 MB/s) - ‘setup-repos.sh’ saved [5268/5268]

Step 2

sh setup-repos.sh

Output:

Setup repository? (y/N) y
  Downloading Webmin key ..
  .. done
  Installing Webmin key ..
  .. done
  Setting up Webmin repository ..
  .. done
  Cleaning repository metadata ..
  .. done
  Downloading repository metadata ..
  .. done

Now you can run apt update and then apt upgrade.