When I was at Qt I spent a decent amount of time porting the native rendering engine from Qt4 to Qt5. It should be available and work relatively well. I have retired from the Qt project, but it looks like the code is still there in the repo. [1] You might need to tell the configure script to build it. To use it, set the QT_XCB_NATIVE_PAINTING environment variable.
[1] https://code.qt.io/cgit/qt/qtbase.git/tree/src/plugins/platf...
Things seems to be going backwards in this area..