This posts looks very old, but still not answered. I think keypress event is not working properly in QtWebEngineView. Did you tried the evenfilter mechanism. I tried and it is working well in my Qt WebEngine project. https://wiki.qt.io/How_to_catch_enter_key
Maybe QtWebEngine component was not installed correctly.
Go to your Qt 5.8 binaries folder (in my case is C:\Qt\Qt5.8.0\5.8\msvc2015\bin) and check if you have the QtWebEngine components there, the image below shows those components highlighted in red.
If you don't have those components installed in your file system open the Maintenance Tool (located in C:\Qt\Qt5.8.0 in my case) and add it those components checking the option highlighted in red in the image below
The concept of QWebEngineView::findText() is really, really weird. If you’re looking for specific text on a webpage, you want to know the searched for text is there NOW..not when some callback function gets around to it.