The textureprovider example should be removed. It is using OpenGL directly to demonstrate compressed texture support.
This is bad on multiple levels now:
1. it uses OpenGL directly,
2. it reimplements something that is built-in since 5.12 (compressed texture support)
It is unfortunate that we lose the example of implementing a custom QSGTexture provider, but removing it is the best choice for now, it seems.