Querying Odata from Power BI (Version: 2.70.5494.761 64-bit (june 2019.)) does not fold when you do Group by and Sum.
Example:
let
Source = OData.Feed("http://services.odata.org/northwind/northwind.svc/"),
Order_Details_table = Source{[Name="Order_Details",Signature="table"]}[Data],
GroupedRows = Table.Group(Order_Details_table, {"OrderID"}, {{"Count", each List.Sum([Quantity]), type number}})
in
GroupedRows
It recives all the rows