I don’t think it is that straight forward. Looking at a couple of my runs on that and the NP vs FTP I did in the workout, the NP is about 92% of the FTP I did for the workout.
Part of that comes from the pure fact that the 4 intervals are split with recoveries, not to mention the warm up and cool down at the end.
It will take a bit more introspection to consider how you felt during the 100% of FTP efforts and considering how it would feel if you did one or more of those back to back with no recovery.
This is about ball parking the FTP value by feel more than some other semi-automatic data comparison via workout.