Well, if you read the Marlin page about Model Predictive Control you have the Manual Tuning section that says " If M306 T doesn’t work –e.g., with positive temperature coefficient (PTC) hotends– MPC can be configured manually."
I was also excited to try this new feature when I got the same MPC Autotune interrupted! message.
The manual procedure seems too complicated. I’ll buy a Trianglelab NTC 100K B3950 thermistor for my Ender 3.