QtWebEngine pages like the Welcome page or the help pages are not shown on Ubuntu 22.04 when using our Ubuntu 20.04 installers. I found a workaround by setting the environment variable QTWEBENGINE_DISABLE_SANDBOX=1. However it is a pretty ugly fix and we should check if we find another solution despite creating separate installers for Ubuntu 22.04 again.
Installers are built with Qt 5.12.12.
QTWEBENGINE_DISABLE_SANDBOX=1 is equal to QTWEBENGINE_CHROMIUM_FLAGS="--no-sandbox". While trying to debug the issue, I noticed that the following workaround to have the WebEngine renderer and plugins in the same process as the browser works as well: QTWEBENGINE_CHROMIUM_FLAGS="--single-process". It is and sounds less scary compared to disabling the sandbox. As a fix, we could change our start shell scripts on Linux to set the environment variable for the call of the application.
We may even be able to do it in code, according to the Qt documentation: QTWEBENGINE_CHROMIUM_FLAGS can also be set using {qputenv} from within the application if called before QtWebEngineQuick::initialize().