Cannot reproduce with Qt 6.6.2. Possibly a Qt 6.7 regression.

plasma-discover
libs QList("/usr/lib/x86_64-linux-gnu/qt6/plugins", "/usr/bin")
org.kde.plasma.libdiscover: OdrsReviewsBackend: Fetch ratings: true
adding empty sources model QStandardItemModel(0x5735d2867e10)
ASSERT: "isSorted(cats)" in file ./libdiscover/Category/Category.cpp, line 240
KCrash: Application 'plasma-discover' crashing... crashRecursionCounter = 2
KCrash: Application Name = plasma-discover path = /usr/bin pid = 8818
KCrash: Arguments: /usr/bin/plasma-discover 
KCrash: Attempting to start /usr/lib/x86_64-linux-gnu/libexec/drkonqi
QSocketNotifier: Invalid socket 6 and type 'Read', disabling...
QSocketNotifier: Invalid socket 60 and type 'Read', disabling...
org.kde.drkonqi: Mapping found despite product information being provided by the application. Consider removing the mapping entry "plasma-discover"
void ReportInterface::maybePickUpPostbox()
kf5idletime_wayland: This plugin does not support polling idle time
29      ../sysdeps/unix/sysv/linux/poll.c: No such file or directory.
Unable to start Dr. Konqi
void ReportInterface::maybePickUpPostbox()


kinfo
Operating System: KDE neon user 6.0
KDE Plasma Version: 6.0.4
KDE Frameworks Version: 6.1.0
Qt Version: 6.7.0
Kernel Version: 6.5.0-27-lowlatency (64-bit)
Graphics Platform: Wayland
Processors: 2 × Intel® Core™2 Duo CPU E4700 @ 2.60GHz
Memory: 2.8 ГіБ of RAM
Graphics Processor: NVA8

Is this still reproducible? I've downloaded the latest testing ISO and discover seems to start properly.

(In reply to Harald Sitter from comment #3)
> Is this still reproducible? I've downloaded the latest testing ISO and
> discover seems to start properly.

Now the glitch looks like this when the locale is set to uk_UA.UTF-8, discover crashes with the error plasma-discover

libs QList("/usr/lib/x86_64-linux-gnu/qt6/plugins", "/usr/bin")
org.kde.plasma.libdiscover: OdrsReviewsBackend: Fetch ratings: true
adding empty sources model QStandardItemModel(0x62f3e0e5e420)
ASSERT: "isSorted(cats)" in file ./libdiscover/Category/Category.cpp, line 240
KCrash: Application 'plasma-discover' crashing... crashRecursionCounter = 2
KCrash: Application Name = plasma-discover path = /usr/bin pid = 28541
KCrash: Arguments: /usr/bin/plasma-discover
KCrash: Attempting to start /usr/lib/x86_64-linux-gnu/libexec/drkonqi
**
OSTree:ERROR:./libglnx/glnx-local-alloc.h:74:glnx_close_fd: assertion failed: (errno != EBADF)
Bail out! OSTree:ERROR:./libglnx/glnx-local-alloc.h:74:glnx_close_fd: assertion failed: (errno != EBADF)
Unable to start Dr. Konqi
org.kde.drkonqi: The specified process does not exist.

But when I explicitly set the encoding LC_ALL=POSIX plasma-discover, it starts up with a slowdown, but it works

After update see next bugs

plasma-discover
libs QList("/usr/lib/x86_64-linux-gnu/qt6/plugins", "/usr/bin")
org.kde.plasma.libdiscover: OdrsReviewsBackend: Fetch ratings: false
adding empty sources model QStandardItemModel(0x62d7a11cedb0)
ASSERT: "isSorted(cats)" in file ./libdiscover/Category/Category.cpp, line 240
KCrash: Application 'plasma-discover' crashing... crashRecursionCounter = 2
KCrash: Application Name = plasma-discover path = /usr/bin pid = 94423
KCrash: Arguments: /usr/bin/plasma-discover 
KCrash: Attempting to start /usr/lib/x86_64-linux-gnu/libexec/drkonqi
org.kde.drkonqi: Mapping found despite product information being provided by the application. Consider removing the mapping entry "plasma-discover"
kf5idletime_wayland: This plugin does not support polling idle time

[1]+  Stopped                 plasma-discover

Dear Bug Submitter,

This bug has been in NEEDSINFO status with no change for at least
15 days. Please provide the requested information as soon as
possible and set the bug status as REPORTED. Due to regular bug
tracker maintenance, if the bug is still in NEEDSINFO status with
no change in 30 days the bug will be closed as RESOLVED > WORKSFORME
due to lack of needed information.

For more information about our bug triaging procedures please read the
wiki located here:
https://community.kde.org/Guidelines_and_HOWTOs/Bug_triaging

If you have already provided the requested information, please
mark the bug as REPORTED so that the KDE team knows that the bug is
ready to be confirmed.

Thank you for helping us make KDE software even better for everyone!

Today a little bit of improvement after getting the latest updates:

in konsole:
$ plasma-discover
libs QList("/usr/lib/x86_64-linux-gnu/qt6/plugins", "/usr/bin")
org.kde.plasma.libdiscover: OdrsReviewsBackend: Fetch ratings: true
adding empty sources model QStandardItemModel(0x5ff64a0d10a0)
qrc:/qt/qml/org/kde/discover/qml/DiscoverWindow.qml:330:5: QML OverlaySheet: Binding loop detected for property "implicitHeight"
qrc:/qt/qml/org/kde/discover/qml/BrowsingPage.qml:17:1: QML BrowsingPage: Created graphical object was not placed in the graphics scene.
PackageKitBackend: No distro component found for "org.kde.neon.neon"
(process:4763): GLib-GObject-WARNING **: 07:24:43.480: cannot register existing type 'SoupMessage'
(process:4763): GLib-GObject-WARNING **: 07:24:43.480: cannot add private field to invalid (non-instantiatable) type '<invalid>'
(process:4763): GLib-CRITICAL **: 07:24:43.480: g_once_init_leave: assertion 'result != 0' failed
(process:4763): GLib-GObject-WARNING **: 07:24:43.480: ../../../gobject/gsignal.c:1760: parameter 1 of type '<invalid>' for signal "SoupSession::request-queued" is not a value type

Now Discover window appears but when I try to click on About or Settings it hangs
and the window title bar shows "Home -- Discover (Not Responding)"

info
Operating System: KDE neon Testing Edition
KDE Plasma Version: 6.0.4
KDE Frameworks Version: 6.3.0
Qt Version: 6.7.0
Kernel Version: 6.5.0-35-generic (64-bit)
Graphics Platform: Wayland
Processors: 4 × Intel® Core™ i3-2120 CPU @ 3.30GHz
Memory: 3.8 GiB of RAM
Graphics Processor: NV108

plasma-discover
libs QList("/usr/lib/x86_64-linux-gnu/qt6/plugins", "/usr/bin")
org.kde.plasma.libdiscover: OdrsReviewsBackend: Fetch ratings: true
adding empty sources model QStandardItemModel(0x5c78ad388030)
ASSERT: "isSorted(cats)" in file ./libdiscover/Category/Category.cpp, line 240
KCrash: Application 'plasma-discover' crashing... crashRecursionCounter = 2
KCrash: Application Name = plasma-discover path = /usr/bin pid = 22690
KCrash: Arguments: /usr/bin/plasma-discover 
KCrash: Attempting to start /usr/lib/x86_64-linux-gnu/libexec/drkonqi

(process:22690): flatpak-WARNING **: 09:41:22.099: Encountered error checking for commit object 4b74c43501da43798f0c7431d75d39f3e40f09dec137351ed0cf8ee21efd87ad: fstatat(4b/74c43501da43798f0c7431d75d39f3e40f09dec137351ed0cf8ee21efd87ad.commit): Bad file descriptor
**
OSTree:ERROR:./libglnx/glnx-local-alloc.h:74:glnx_close_fd: assertion failed: (errno != EBADF)
Bail out! OSTree:ERROR:./libglnx/glnx-local-alloc.h:74:glnx_close_fd: assertion failed: (errno != EBADF)
Unable to start Dr. Konqi