Prior to 6.3, calling setDiffuse on a Qt3DExtras::QDiffuseSpecularMaterial instance, with a texture as argument, would render the texture on the sibling mesh.  From 6.3 onwards, the same code renders the mesh as black.

The attached tarball demonstrates the problem. On launch it renders a sphere. When "Edit > Add Texture" is invoked, a grayscale texture image is created and used as the sphere's texture.

Under Qt 5 (configure with "cmake -Bbuild -S. -DQT_6=OFF") the texture is applied to the sphere. Under Qt 6 ("cmake -Bbuild -S."), the sphere turns black.