SUMMARY
Applications using qtwebengine (say, kmail) unresponsive on startup when launched on Wayland with Nvidia without using XWayland (running with QT_QPA_PLATFORM=xcb).

STEPS TO REPRODUCE
1.  Launch Plasma Wayland Session
2.  Launch Kmail

OBSERVED RESULT
Window is unresponsive, though process itself does not crash when launched via a terminal.

EXPECTED RESULT
Window accepts inputs and functions as expected.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Fedora 40 release candidate/beta
KDE Plasma Version:  6.0.3
KDE Frameworks Version: 6.0.0
Qt Version: 6.6.2

ADDITIONAL INFORMATION
Output when run via terminal:
qt.dbus.integration: Could not connect "org.freedesktop.NetworkManager" to "stateChanged" : Type not registered with QtDBus in parameter list: QNetworkManagerInterface::NMState
qt.dbus.integration: Could not connect "org.freedesktop.NetworkManager" to "connectivityChanged" : Type not registered with QtDBus in parameter list: QNetworkManagerInterface::NMConnectivityState
qt.dbus.integration: Could not connect "org.freedesktop.NetworkManager" to "deviceTypeChanged" : Type not registered with QtDBus in parameter list: QNetworkManagerInterface::NMDeviceType
qt.dbus.integration: Could not connect "org.freedesktop.NetworkManager" to "meteredChanged" : Type not registered with QtDBus in parameter list: QNetworkManagerInterface::NMMetered
DRM kernel driver 'nvidia-drm' in use. NVK requires nouveau.

The reference to the specific kernel DRM driver is of note here, as programs without QTWebEngine do not have this issue nor display such a message.