oh my god! I can't believe i was so blind! Thanks a lot to both!
I switched the connection back to QWebEngineView. I don't even remember why I thought that sending the signal from QWebEnginePage was a good idea, since i have to delete the pointer not to let it hanging.
Now it seems to work, but pix comes out blank. Perhaps loadfinished is too quick, and triggers before javascript has finished generating the document?
Is there a slower signal? Or perhaps a way to give js a tad more of time to load before calling render? Before using signals and slots I tried to wait it with a loop, but it seems the loop blocks js.