I just tried this on my primary box; same reaction (home screen never shows on plasma discover).

guiverc@d7050-next:~$   plasma-discover
org.kde.plasma.libdiscover: Couldn't find the backend:  "kns-backend" among ("fwupd-backend", "kns-backend", "packagekit-backend", "snap-backend")
fetch ratings! true
adding empty sources model QStandardItemModel(0x559d39cfee80)
kf.kirigami: Failed to find a Kirigami platform plugin
qrc:/qml/Feedback.qml:2:1: module "org.kde.userfeedback" is not installed
no component found for "com.ubuntu.ubuntu"
packagekitqt.transaction: Unknown Transaction property: "Sender" QVariant(QString, ":1.12871")
file:///usr/lib/x86_64-linux-gnu/qt5/qml/org/kde/kirigami.2/ScrollablePage.qml:200:9: QML MouseArea: Binding loop detected for property "implicitHeight"
file:///usr/lib/x86_64-linux-gnu/qt5/qml/org/kde/kirigami.2/ScrollablePage.qml:200:9: QML MouseArea: Binding loop detected for property "implicitHeight"
packagekitqt.transaction: Unknown Transaction property: "Sender" QVariant(QString, ":1.12871")
packagekitqt.transaction: Unknown Transaction property: "Sender" QVariant(QString, ":1.12871")
took really long to fetch PackageKitBackend(0x559d39ce2400)
packagekitqt.transaction: Unknown Transaction property: "Sender" QVariant(QString, ":1.12871")
packagekitqt.transaction: Unknown Transaction property: "Sender" QVariant(QString, ":1.12871")
packagekitqt.transaction: Unknown Transaction property: "Sender" QVariant(QString, ":1.12871")
packagekitqt.transaction: Unknown Transaction property: "Sender" QVariant(QString, ":1.12871")
packagekitqt.transaction: Unknown Transaction property: "Sender" QVariant(QString, ":1.12871")
PackageKit stopped running!

I exited, restart & same effect..
I can use other 'tabs' in the program, just returning to HOME has "Loading..." and four 'bars' that move...

(second load attempt follows & messages from qterminal)

guiverc@d7050-next:~$   plasma-discover
org.kde.plasma.libdiscover: Couldn't find the backend:  "kns-backend" among ("fwupd-backend", "kns-backend", "packagekit-backend", "snap-backend")
fetch ratings! false
adding empty sources model QStandardItemModel(0x5577824aad80)
kf.kirigami: Failed to find a Kirigami platform plugin
qrc:/qml/Feedback.qml:2:1: module "org.kde.userfeedback" is not installed
no component found for "com.ubuntu.ubuntu"
packagekitqt.transaction: Unknown Transaction property: "Sender" QVariant(QString, ":1.12922")
packagekitqt.transaction: Unknown Transaction property: "Sender" QVariant(QString, ":1.12922")
packagekitqt.transaction: Unknown Transaction property: "Sender" QVariant(QString, ":1.12922")
Qt Quick Layouts: Detected recursive rearrange. Aborting after two iterations.
Qt Quick Layouts: Detected recursive rearrange. Aborting after two iterations.
couldn't find ("org.kde.kio") which is supposedly extended by "org.kde.kio.admin"
packagekitqt.transaction: Unknown Transaction property: "Sender" QVariant(QString, ":1.12922")
packagekitqt.transaction: Unknown Transaction property: "Sender" QVariant(QString, ":1.12922")
org.kde.plasma.libdiscover: cannot infer categories from CategoryFilter::AppstreamIdWildcardFilter
packagekitqt.transaction: Unknown Transaction property: "Sender" QVariant(QString, ":1.12922")
kf.kirigami: Could not create delegate for ToolBarLayout
kf.kirigami: file:///usr/lib/x86_64-linux-gnu/qt5/qml/org/kde/kirigami.2/ActionToolBar.qml: Object or context destroyed during incubation
kf.kirigami: Could not create delegate for ToolBarLayout
kf.kirigami: file:///usr/lib/x86_64-linux-gnu/qt5/qml/org/kde/kirigami.2/ActionToolBar.qml: Object or context destroyed during incubation
packagekitqt.transaction: Unknown Transaction property: "Sender" QVariant(QString, ":1.12922")
packagekitqt.transaction: Unknown Transaction property: "Sender" QVariant(QString, ":1.12922")
file:///usr/lib/x86_64-linux-gnu/qt5/qml/org/kde/kirigami.2/ScrollablePage.qml:200:9: QML MouseArea: Binding loop detected for property "implicitHeight"
file:///usr/lib/x86_64-linux-gnu/qt5/qml/org/kde/kirigami.2/ScrollablePage.qml:200:9: QML MouseArea: Binding loop detected for property "implicitHeight"
Qt Quick Layouts: Detected recursive rearrange. Aborting after two iterations.
Qt Quick Layouts: Detected recursive rearrange. Aborting after two iterations.
org.kde.plasma.libdiscover: cannot infer categories from CategoryFilter::AppstreamIdWildcardFilter
file:///usr/lib/x86_64-linux-gnu/qt5/qml/org/kde/kirigami.2/ScrollablePage.qml:200:9: QML MouseArea: Binding loop detected for property "implicitHeight"
file:///usr/lib/x86_64-linux-gnu/qt5/qml/org/kde/kirigami.2/ScrollablePage.qml:200:9: QML MouseArea: Binding loop detected for property "implicitHeight"