I've seen the Starlink satellites the past couple nights. The first few reminded me of fighter jets in trail, but after the 10th one I realized what I was seeing. Very cool!
I have only ever seen one thing while flying that I cannot explain. It was a flashing light on the ground and not a UFO. I am positive it was manmade, but I've never been able to figure out what it was or why it was behaving the way we observed.