Has an AFL game ever ended 84-21?
Exactly once. On July 9, 2021, Essendon beat Adelaide 84-21, and no AFL game before or since has ended that way. When it happened it was a scorigami, the first 84-21 in league history.
That makes 84-21 the 3836th most common final score out of 6,607 that have ever occurred in AFL. One point away, 85-21 has happened never and 84-22 has happened 1 times.