Hello,
ECM middleware class is now part of newer packages in STM32Cube repository. In some packages you can find also example projects, like in F7 one, which you can find on following path (depending also on your CubeMX setting):
...\STM32Cube\Repository\STM32Cube_FW_F7_V1.16.0\Projects\STM32746G-Discovery\Applications\USB_Device\CDC_ECM_Server
Best regards,
Lubos
