Porting OpenGLunderQML example to PySide fails

I came across a number of issues while porting https://code.qt.io/cgit/qt/qtdeclarative.git/tree/examples/quick/scenegraph/openglunderqml?h=5.15 to PySide2.

The port is trying to be as close as possible to the original (even comments have be transferred). Right now, the output is glitchy (see attached png) but it's actually rendering through OpenGL. The main.py file can be executed directly with python main.py to reproduce.

The two main.py and main.qml files contains various FIXME. Here is a summary:

1. window.rendererInterface() leads to 'PySide2.QtQuick.QQuickView' object has no attribute 'rendererInterface'
2. initializeOpenGLFunctions() crashes
3. program.setUniformValue("t", float(self._t)) is not recognized as a valid prototype
4. the output is glitchy (maybe messed up something in the OpenGL calls but I don't see it)
5. in the QML, the SequentialAnimation on t can not be made

Any hint/directions? I'm trying to build a PySide2+QML application that use an external engine with different backends (OpenGL, Vulkan, etc), and this example would be a good first step in that direction.