Hi this might be due to the new Qt RHI, an abstraction over OpenGL, Vulkan, Metal, DirectX (might have forgotten some or mentioned some that shouldn't be).
Qt Quick will no longer be speaking directly to OpenGL but there will be an abstraction on top of it to ensure compatility with other graphical stacks.
You will get more info about this by googling around or watching this webinar : https://www.youtube.com/watch?v=eInD6H4XrpM