"Failed to get a list of devices: 'Forbidden'", when list new printers on Kubuntu20.04

I installed a fresh Kubuntu-20.04, and created the first user(jacky) by means of the installer of Kubuntu, then I created the second user(leon), by using cmd-line tool "adduser", and adding it into the group "root" and "libvirt".

Both of these two users can login KDE and do things normally, but only jacky can setup printers of the system. When I login with leon and open "System Setting -> Printers", and click the button "Click here to add a new printer", I always get a error msg:

Failed to get a list of devices: 'Forbidden'

in a poped-up dialog box "Add a New Printer". If with the user jacky do so, no error occurs.

I guess these two users are different, but I don't know what difference is there and how fix it. Any hints?

Please Forgive my English!!!

Try adding your user "leon" to group "lpadmin" and log out and re-login again. I can't test this at the moment.

I'm getting the same error in openSUSE 15.2 KDE for my only user. In the journalD log, I see kde-add-printer libkcups: CUPS-Get-Devices last error: 1025 Forbidden. I'm guessing it's the same for you?