Re-writing my reply, I had a few things wrong.
This should be what you need, or very close to it:
With({wdata:Filter(Master_Data, StartsWith(Requestor_Name, TextInput2.Text), Allocated_To = User().FullName)}, ClearCollect(colGridData, Filter(wdata, !("Completed" in Mail_Status.Value ), !("discard" in Mail_Status.Value ))));
One Filter statement allows multiple logic checks, like this:
Filter(Data_Source, Len(Description) >5, Len(Name) >5, Status = 'Status (Case Types)'.Active)
You correctly started a Filter Statement, but then rather than giving it a second logic check, you gave it another Filter:
Filter( wData, !("Completed" in Mail_Status.Value ),Filter( wData, !("discard" in Mail_Status.Value ) )