How can I use the filter in the IDriveItemDeltaRequest correctly with C# and ASP.NET Core?
The interface says the following about filters
// Adds the specified filter value to the request.
//
// value:
// The filter value.
//
// The request object to send.
IDriveItemDeltaRequest Filter(string value);
I thought it was not possible to filter with Graph delta using Onedrive?
As per the official documentation, $filter is not supported. This method supports the $select, $expand, and $top OData query parameters to customize the response.
Being said that, consider filing user voice so that same could be considered for future implementation.