From the Super Mario Wiki, the Mario encyclopedia
Hot-air balloons are recurring objects in the Mario Kart series, usually serving as background objects.
Mario Kart 7
Hot-air balloons first appear in Mario Kart 7, appearing in Daisy Hills. They either have red and white squares, dark and light blue horizontal lines, or vertical yellow and orange lines. Touching a balloon will cause the player to bounce off it.
Mario Kart 8 / Mario Kart 8 Deluxe
Hot-air balloons reappear in Mario Kart 8 and Mario Kart 8 Deluxe, appearing as background objects in Royal Raceway and Mount Wario. In Royal Raceway, balloons are designed after Princess Peach, Princess Daisy, and Rosalina, and have Toads standing inside the balloons' baskets, while the balloons in Mount Wario are designed after Mario, Luigi, and Wario. Touching a balloon will push back the player.
Mario Kart Tour
Hot-air balloons reappear in Mario Kart Tour. They appear in all versions of Daisy Hills, DS DK Pass R/T, DS Koopa Troopa Beach R, Wii Maple Treeway T, all versions of Paris Promenade, 3DS Rock Rock Mountain R, all versions of Royal Raceway (except for the reverse variation), Vancouver Velocity R, and GCN Yoshi Circuit T. They also appear in a Glider Challenge in Yoshi Circuit in the Paris Tour and a Do Jump Boosts challenge in DK Pass in the Winter Tour. Landing on top of a balloon gives the player a Jump Boost. Balloons appear in the same patterns as they did in Mario Kart 7, and can also have vertical purple and white lines. In Vancouver Velocity R, the balloons contain Snowpeople; however, the balloons in N64 Royal Raceway no longer contain Toads.