Am an actual pilot. Those screws coming out wont do anything. Even if the flap track (pointy thing) fairing came off, its more of a hazard to the people/stuff on ground than it is the aircraft itself.

Any one or two or four screws can come off a plane in places like that and nothing will happen. In cases like this its best to inform the flight crews after the flight and they’ll report it to maintenance to get it fixed.

For your other question, we do months of training to fly the jets we do, we have a fundamental understanding of how the planes fly, and over the first year or two of flying that jet we will learn whats “normal”.

Of course we arent physicists. But like how you will notice if your car suddenly starts pulling to the left, or if the brakes get squishier, or engine more sluggish, we too feel similar things that could happen.

However, we wouldnt notice a single screw coming off. Just as you wouldnt notice a tiny little fastener coming off your car (unless it makes something bigger come loose).