Unsure if this is a packaging issue but I thought I post this here as well to let you know.
On Arch, upgrading appstream and appstream-qt from 1.1.3-1 to 1.1.4-1 breaks the Flatpak backend of Discover. On startup, the following message is displayed:
Arch Linux is not configured for installing apps through Discover--only app add-ons. To use Discover for apps, install Flatpak using the pacman package manager. Review Arch Linux's packaging for Discover"
Launching Discover with the Flatpak backend forced on results in this message:
> plasma-discover --backends flatpak-backend
org.kde.plasma.libdiscover: error loading "flatpak-backend" "The library /usr/lib/qt6/plugins/discover/flatpak-backend.so could not be loaded: /usr/lib/qt6/plugins/discover/flatpak-backend.so: undefined symbol: _ZNK9AppStream9Component9addBundleERKNS_6BundleE" QJsonObject({"IID":"org.kde.discover.6.7.3.AbstractResourcesBackendFactory","archlevel":1,"className":"FlatpakBackendFactory","debug":false,"version":396032})
org.kde.plasma.libdiscover: Didn't find any Discover backend!
qrc:/qt/qml/org/kde/discover/qml/DiscoverWindow.qml:124:5: QML Shortcut: Shortcut: Only binding to one of multiple key bindings associated with 15. Use 'sequences: [ <key> ]' to bind to all of them.
org.kde.plasma.libdiscover: OdrsReviewsBackend: Fetch ratings: false
looking up wrong category or too early "Games"
looking up wrong category or too early "Development"
looking up wrong category or too early "All Applications"
qt.qpa.services: Failed to register with host portal QDBusError("org.freedesktop.portal.Error.Failed", "Could not register app ID: Connection already associated with an application ID")
A downgrade of both appstream packages to 1.1.3 fixes the issue.