In the Kalos games, all three starters have secondary types. Chesnaught has Fighting, Delphox has Psychic, and Greninja has Dark.
In the Alola games, all three starters have secondary types as well. Decidueye has Ghost, Incineroar has Dark, and Primarina has Fairy.
In Legends: Arceus, Hisuian Decidueye has Fighting, Hisuian Typhlosion has Ghost, and Hisuian Samurott has Dark.
In the Paldea games, Meowscarada has Dark, Skeledirge has Ghost, and Quaquaval has Fighting.
Therefore, the Sinnoh games are no longer the only ones with all three starters having secondary types.