It comes from a 4 hours highway trip.
Trip was back and forth, to compensate for road altitude and SOC differences, as SOC average value was 60.49%.
The chart starts at 80 km/h where EV is not available, so this is indeed only ICE consumption.
Interesting curves here are the bold blue one, representing average RPM at each given speed, and the yellow one, average fuel flow at the same speed.
We can note that until a little more than 90 km/h, the fuel curve follows RPM curve by staying under it. After that, fuel flow begin to grow with a steeper angle.
I suspect aerodynamic drag may be the primary suspect here.
Chart with added load and enhanced grid:
Chart from a user willing to drive way faster than me:
Relationship between Fuel and Speed