Upon checking your documentation here: https://mongodb.github.io/mongo-csharp-driver/2.14/reference/driver/expressions/#week there are no any example for using $week in c#.

Please help we really want to use the $week for our group by. 

We would like to request to mongoDB .net driver Team to create a natively $week operator in group by c#, perharps using your own syntax library without depending on the c# Week property. I dont think c# will add the Week property in the DateTime class.

Related forum issue thread: https://www.mongodb.com/community/forums/t/group-by-week-in-c-library/197509