SUMMARY
I am getting following error whenever I am trying to remove or install something from Discover.

You have no authorization to execute this operation

STEPS TO REPRODUCE
1. Open Discover
2. Click on Install for any application
3. Click on Remove for any installed application

OBSERVED RESULT
Results in a prompt that either says "You have no authorization to execute this operation" or "Failed to obtain authentication"

EXPECTED RESULT
It should install or remove the application. Further, it should prompt for root password before performing these operations.

SOFTWARE/OS VERSIONS
Windows: 
macOS: 
Linux/KDE Plasma: Kubuntu 20.10
(available in About System)
KDE Plasma Version: 5.19.5
KDE Frameworks Version: 5.74.0
Qt Version: 5.14.2

ADDITIONAL INFORMATION

Kubuntu:~$ lsb_release -r
Release:        20.10
Kubuntu:~$ uname -a
Linux Kubuntu 5.8.0-33-generic #36-Ubuntu SMP Wed Dec 9 09:14:40 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux
Kubuntu:~$ plasma-discover
qrc:/qml/Feedback.qml:2:1: module "org.kde.userfeedback" is not installed
kf.newstuff.core: Your configuration file uses an old version of the kpackage support, and should be converted. Please report this to the author of the software you are currently using. The package type, we assume, is "Plasma/Theme"
kf.newstuff.core: Your configuration file uses an old version of the kpackage support, and should be converted. Please report this to the author of the software you are currently using. The package type, we assume, is "Plasma/LookAndFeel"
kf.newstuff.core: Your configuration file uses an old version of the kpackage support, and should be converted. Please report this to the author of the software you are currently using. The package type, we assume, is "KWin/Effect"
kf.newstuff.core: Your configuration file uses an old version of the kpackage support, and should be converted. Please report this to the author of the software you are currently using. The package type, we assume, is "KWin/WindowSwitcher"
kf.newstuff.core: Your configuration file uses an old version of the kpackage support, and should be converted. Please report this to the author of the software you are currently using. The package type, we assume, is "Plasma/Wallpaper"
invalid kns backend! "/usr/share/knsrcfiles/servicemenu.knsrc" because: "Config group not found! Check your KNS3 installation."
kf.newstuff.core: Your configuration file uses an old version of the kpackage support, and should be converted. Please report this to the author of the software you are currently using. The package type, we assume, is "Plasma/Comic"
kf.newstuff.core: Your configuration file uses an old version of the kpackage support, and should be converted. Please report this to the author of the software you are currently using. The package type, we assume, is "Plasma/LookAndFeel"
kf.newstuff.core: Your configuration file uses an old version of the kpackage support, and should be converted. Please report this to the author of the software you are currently using. The package type, we assume, is "KWin/Script"
invalid kns backend! "/usr/share/knsrcfiles/ksysguard.knsrc" because: "Config group not found! Check your KNS3 installation."
kf.newstuff.core: Your configuration file uses an old version of the kpackage support, and should be converted. Please report this to the author of the software you are currently using. The package type, we assume, is "Plasma/Applet"
adding empty sources model QStandardItemModel(0x5635b65df320)
QObject::connect(AbstractReviewsBackend, ResourcesModel): invalid nullptr parameter
org.kde.plasma.libdiscover: Couldn't find a category for  "fwupd-backend"
file:///usr/lib/x86_64-linux-gnu/qt5/qml/org/kde/kirigami.2/private/globaltoolbar/PageRowGlobalToolBarUI.qml:49:9: QML PrivateActionToolButton: Binding loop detected for property "checkable"
Fwupd Error:  Remote  vendor-directory has no cache signature!
percentage cannot be calculated
percentage cannot be calculated
percentage cannot be calculated
percentage cannot be calculated
percentage cannot be calculated
percentage cannot be calculated
percentage cannot be calculated
percentage cannot be calculated
percentage cannot be calculated
PackageKit error: PackageKit::Transaction::ErrorNotAuthorized "You have no authorization to execute this operation" "Failed to obtain authentication."