Direct OpenGL usage is to be removed, together with the QSG_RHI environment variable. From that point on the default behavior will be as if one ran with QSG_RHI=1.
This also involves doing the todos that are marked as ### Qt 6 in the QSGMaterial and QSGTexture related parts for instance. Incompatible / not relevant APIs (such as QSGMaterialShader, textureId() type of accessors, etc.) are to be removed. These may need deprecations in 5.15 first.
This may present breakages on all levels, in other modules as well, so all in all the work here may be a bigger piece to execute properly. Note the separate tasks for documentation.