Forza Horizon 4 is adding a free Battle Royale mode tomorrow called The Eliminator.
Basically, the mode has 72 players randomly dropping around the map in a red Mini Cooper and you must work your way to eliminate other players, and upgrade your car (either by taking theres or finding random car drops).
You eliminate players in head to head races that will have you driving 1 on 1 against other drivers in a race to get to a certain spot on the map. A purple storm also closes in forcing you towards other players.