The Qt Quick documentation should be carefully checked for things that need to be changed, updated or removed due to the QRhi-based rendering path.
In 5.14 the scenegraph-related pages have been updated and rephrased as much as possible to apply to both rendering paths, but in 6.0 this needs a lot bigger effort in case the direct OpenGL code path is going away.
For example, consider ShaderEffect. Now that the default (and the only?) choice is to reference .qsb files, the documentation needs a massive revision to reflect this.