I disagree with this; mathematically, sure it is “correct” that it is giving the RMS value.

However, the app was set to DC mode and thus should not silently use RMS (currently there’s no indicator nor option to use RMS in DC or V-avg or Vp, etc.)

Think of a black-box scenario.
The resulting plotted graph isn’t enough to indicate that what is being measured is a rectified AC let alone that the resulting units are in VDCrms. Without some sort of indicator, there’s no way to tell.
It is essentially saying that VDCrms = VDC

Also “rectified AC” is technically DC (it’s no longer alternating)