The Boruto manga has unfortunately skipped something very important, the reason why the series' main characters just happened to get assigned to the same team number as Naruto, Sasuke, and Sakura did in Naruto. However, the anime actually thoroughly explained how Boruto, Sarada, and Mitsuki got assigned to Team 7, and it's much more nuanced than manga fans could possibly imagine.
https://screenrant.com/boruto-team-name-more-important-manga-fans-realize/