The supra's don't have a fuel pressure sensor fitted, There must be something wrong your Torque app.
I have a vvti supra and the torque app and I do not get fuel pressure because there is no sensor.
The base fuel pressure is about 3 bar / 43 psi, base pressure is when the pump is running and there is no vac/pressure hose connected to the regulator.
The vac/pressure line is there to keep the fuel pressure constant to the manifold pressure, so if you have 1 bar of boost the fuel pressure will rise to approx 4 bar and the same happens when the manifold is in vacuum ie -1 bar vac the fuel pressure will be 2 bar.
So the max pressure that should be seen on a std bpu supra would be about 4.5 bar.
As you have the torque app I would use this to check the long term fuel trims (I will not explain about fuel trims there is plenty on info on the net) if the fuel trim is in the negative it means that the ecu is pulling fuel to keep it running at the right AFR, if this is the case it could be the fuel pressure is higher than normal or the O2 sensor is faulty along with other reasons.
apparently there is not one long term fuel trim used on a global scale, but several. Not sure how to read them all. Maybe one of the toyota ecu guru's could answer?
The fuel pressure regulator in the stock supra can not be adjusted and it is easily replaced ( which I doubt there is anything wrong with it ) and you can check the fuel pressure, one way would be to remove the outlet connection on the fuel filter and place in a Tee fitting for a pressure gauge, and before you ask I don't what size threads etc to use.
The O2 sensor keeps the fueling at the correct AFR for normal running but is ignored when running in the higher boost area but is used to set the short term fuel trim which in turn adjusts the long term fuel trim if needed, and as far as I know the long term fuel trim is used when in higher boost area.
It would not hurt putting in a new 02 sensor as this may help the fueling at higher boost levels if the sensor is out of spec.
In your screenshot of the fuel pressure gauge what are the numbers along the bottom line supposed to mean? ( 1 to 9 )
Also looking at the spark plug is not meaningful as far as I aware, not unless the engine was switched off at the time it was running rich and not allowed to idle etc.
If you get this sorted please post up the answer to the problem as it might help others with the same/similar problems.
hope this helps.
Regards Chris.