A credible Genshin Impact leaker has revealed that miHoYo has apparently made the decision to give more attention to Lumine instead of Aether through their media accounts.
At the start of your Genshin Impact journey, the game allows you to choose your main character. The choice can be made between two siblings - Lumine or Aether. If you choose Lumine, your main quest will be to find your brother who may end up being the main villain of the game.
This choice doesn't impact the flow of your story at all since you're basically choosing which character will be appearing during the game's main story cutscenes. In both scenarios, you are referred to as the Traveler.
A recent post made by a credible Genshin Impact leakers revealed that starting with the anniversary update, the Genshin Impact official media accounts will start to portray Lumine as the main character more often. Apparently, this wasn't the case previously and Aether took that spot most of the time leaving Lumine to be the villain.
miHoYo's decision to bring more balance to the table seems fair since there are many players who chose Lumine as their main character, especially during the earliest phases of the game when there was a popular belief that playing with her increases your chances to pull a five-star character.
The Traveler isn't one of the strongest characters in the game at the moment. Many players and tier lists consider him to be either C or D tier. He can equip two different elements at the moment, Anemo and Geo. Each of the elements represents the region they were acquired in, Anemo for Monstadt and Geo for Liyue.
With the upcoming introduction of the new region Inazuma, the main character could make a return to many players' main parties. The representative element of Inazuma is Electro which means that the traveler will be able to use the new element fairly soon.