Hi, one major issue is that QtWebEngine does not work on Wayland at this time, at least not if it is built with desktop OpenGL. See: https://bugreports.qt.io/browse/QTBUG-55384
This affects kdepim applications (at least KMail) and also some Qt applications developed outside of KDE infrastructure (QupZilla, the Calamares webview module, etc.). Kevin Kofler