What happened to the young man Eutychus while Paul preached late into the night at Troas?

Answer: Fell asleep and fell out a window

Sinking into a deep sleep as Paul talked on, Eutychus fell from the window and was picked up dead, but Paul said, "He is still alive!"

“And a certain young man named Eutychus, seated in the window, was sinking into a deep sleep as Paul talked on and on. When he was sound asleep, he fell from the third story and was picked up dead.”— Acts 20:9 (BSB)