It just uses GDI_CLASSIC for DWRITE_MEASURING_MODE [1] and DWRITE_RENDERING_MODE [2] in that case. No actual GDI in sight.

[1] https://learn.microsoft.com/en-us/windows/win32/api/dcommon/...

[2] https://learn.microsoft.com/en-us/windows/win32/api/dwrite/n...