Forza Horizon 5's first expansion is indeed a racing game.
The latest update adds a new monthly Rivals event featuring electric vehicles. The event will debut with Season 9, and will feature a different EV each month. You can earn festival playlist points just by setting a clean lap time in each monthly event.
The new Forza Horizon 5 patch also adds co-op for Horizon Story events, which s up to six players. Convoy leaders can host any of the Horizon Stories they've already unlocked, and the highest score earned by a member of the convoy will be applied to everyone in the party. If you a convoy and participate in a Horizon Story event, that event will be marked as completed when you return to your own session.
PC players also have a new graphics option included in this patch. The latest update adds temporal anti-aliasing to the multi-sample anti-aliasing options already present in Forza Horizon 5. As Playground Games explains, this method of anti-aliasing reduces shimmering and captures additional detail as it smooths out jagged edges in the picture, and it's a good option when running the game on lower screen resolutions.
The full list of new cars and gear, as well as the complete patch notes, are all available over on Steam.