Elo boosting in League of Legends is not illegal in most parts of the world, but it can result in penalties and account bans by Riot Games.
If you have heard of rank boosting, Apex Legend’s fastest ranking method in the last years, you can read this article to learn all about it
CS2 (CSGO) Rank Boosting Explored: discover what rank boosting is, which are the best boosting sites, how safe they are and how NOT to get banned.