I assume you have completed the flight by now. What did you do? I think many RNP approaches are marked as rnav only with the required navigation accuracy mentioned somewhere in the chart. So basically, you will need to find that required accuracy value and monitor you navigation accuracy in fms during the approach and if it goes above the required number, probably you need to do a missed approach. And AS I understand, MSFS does not model decreased navigation accuracy, so in msfs, RNP and RNAV are essentially same. Note that I am not a real-world pilot but told you all this from my simming experince int the last couple of years. So, i may be very wrong here with some small details.