Unfortunately, like most other details about the upcoming game, we don’t know which Legendary Pokémon will don the covers of the respective titles — but thanks to a riddle from known Pokémon leaker @Riddler_khu on Twitter, we do have some hints.
In some instances, like in Pokémon Sword and Shield, the Legendary Pokémon will share similar themes and designs — but this isn’t always the case. According to Riddler, Scarlet and Violet will have very different Legendary Pokémon.
Source: https://www.distractify.com/p/what-legendary-pokemon-in-pokemon-scarlet-violet