There has never been an official forfeit in NFL history. It looked for a while like we might get one with the Tennessee Titans.
The NFL had threatened forfeiture of games if there were COVID-19 protocol violations. Reports said the Titans were having informal workouts after positive tests and the NFL saying they couldn’t gather. The NFL waited until Tuesday night to play, Tennessee was clear of any more positive tests, and they played (and beat) the Buffalo Bills. The NFL never said what would have happened if the game couldn’t be played, but a forfeiture was likely an option.