Thank you to "Brograph Tutorials".

In this tutorial, you will learn how to render out motion vector files in C4D and bring them into AE and use the RSMB plug in for motion blur.

*Note: The author forgot to set his project to 16 bpc of floating point which removes a lot the need the smooth the motion vector pass (why he uses a blur) particularly as resolution increases.

If you work in floating point in AE, you could also use shift channel instead of set matte.
You can also do all the MV pre-processing  with RE:Fill Alpha or RE:Fill choke if you have that.