Copy pepflashplayer.dll and manifest.json from Google Chrome to the directroy of exe.
Then I also set
QWebEngineSettings::globalSettings()->setAttribute(QWebEngineSettings::PluginsEnabled, true);

And do it manually with command line,
--ppapi-flash-path=the path of the dll

the right click of mouse and hotkey of windows cannot work, anyone knows the reason?
If there is official solution of flash support?

example: http://210.14.132.253/flash/