I found a solution to this issue after much trial and error. I am fairly certain this will need to be done for anyone who is attempting to notarize a macOS application using the QtWebEngine. Hopefully this will save someone some time in the future.
The solution for me was to sign the QtWebEngineProcess with with the com.apple.security.cs.disable-executable-page-protection exception. Here is the process.
Sign the main application with the following command
This may sound weird but I play around with it some more and it was calling another method. I changed some of the code in that method and then downloadRequested got called. I guess something went squirrelly in the QT engine.
If you have to stay on MinGW then you should build the QtWebkit module. QtWebEngine can only be built following the constraints of the Chromium project which means that currently only VS2017 is supported.
So I finally figured it out. It appears to fix the " Unrecognized Content-Security-Policy directive 'disown-opener" error you would have to incorporate the html tag attribute "rel=noopener" in each link tag. However since I want to download html webpages from other sources it would be a bit hard to change each link.
Instead after some trial and error I found that this header "Upgrade: websocket" fixed the issue.
I manage to resolve by upgrading to qt5.12 and Microsoft visual studio 2017. However, when I want to call an external keyboard (a separate exe file) . It is always been block by QtWebengineprocess.exe, how to bring my external keyboard forward?
I hope I understand your problem.
Attention, since reference is made to a fake url it generates error in the log.
@leenamiettinen thanks for responding. Yes, I was referring to that page. But the point is that statement is included a part of the second paragraph that refers to Chromium and third party licenses. So, it seems to me that "LGPLv2.1" in that sentence is applicable only to the Chromium and related third parties modules (but not to the rest of Qt modules also included in QtWebEngine).
Update: it seems that calling the setUrl on the constructor of the QMainWindow the page works fine; if I call the method later (even just before the main window .show() method) the repaint events don't get called