I found out that the engine will shut down after entering negative G for 5 seconds (flying inverted), and I have to level out the jet and wait for the engine restart. However, I saw the JF17 was doing a 5~6 seconds inverted flight during the Paris airshow and the jet immediately doing an aggressive maneuver after that, so the engine was not stop operating IRL after the 5 seconds inverted flight.
Thus, I think the available time for inverted flight in game is shorter than in real life.
Please check on this if you have time, thank you. Here is the link of the video. The inverted flight is on 3:30-3:40 in the video.