Back when I was friendly with win32 and co I heard from one or more of them that 7, when paired with a WDDM 1.1 driver and a capable card, uses DirectX 11 for Aero. I think they would know their shit. Could test with the AMD driver and deleting the DX11 dll on 7.
At the uncertainty of making a new thread or not, i'll be replying you here:
I have analyzed DWM's function calls and it does seem rendering is entirely comprised of D3D10.1 calls (namely D3D10CreateDevice1 for initialization, ID3D10Buffer::Map, ID3D10RenderTargetView::Release, ID3D10Texture2D::Release, ID3D10ShaderResourceView::Release for rendering & other related tasks). While i have observed a very few D3D11 calls, they seem to be used exclusively for checks, only done at the beginning and not used ever again after this initial phase of the compositing engine. I am also not aware of any kind of interoperability between DX10 and 11 that allows running ID3D10 functions inside a D3D11 context. (Likely) There is no 9Ex fallback mode on Win7, as it is probably not even needed. Direct3D10.1 can run on feature level 9_1 hardware providing the renderer code was programmed accordingly (not using hardware features not available in feature level 9_1), which this is the case, so it can run on the same hardware as Vista, providing the driver vendor wasn't lazy enough to forget to implement D3D10.1 on their WDDM drivers for their legacy GPUs (if i'm not mistaken, GeForce 5 FX WDDM drivers never implemented D3D10 so there is that (there is a chance those can only run aero under vista, unless something escapes my knowledge)(further research needed), intel probably neglected some of their older GPUs as well).
Vista also uses exclusively 9Ex. Tests with RivaTuner further confirm my findings (attached images).
Read the latest blog post at my website for all the technical details:
http://neonfloppy.sytes.net/blog/2022-12-25/