Unfortunately that’s the one thing I don’t have any more info than what I gather from the same posts by PhilipsNono.
The trapezium or Vertical Keystone Correction is available for all inputs and uses, works via the hardware. The 4 corner correction is however only available in the Android OS and apps within, which has been addressed by giving better explanation of the limitations (INFO: Limitations of features for HDMI and USB-C inputs)
Please don’t worry about the unit or its features, not all is as bad as some make it out to be, not all is as some expected it to be or were promised it would be, but in the end it is a nice, portable, self-contained unit.