@Lal_S The decision on what becomes a warning is @Ukang_a_Dickson's, but I don't think pyxform (the library that powers XLSForm Online/Offline) should warn when notes are required.
Required notes can be useful. For example, I like to use them like a long message to enumerators. It has to be required because they need to swipe back and fix the issue that triggers that note.