League of Legends level borders are cosmetic frames that surround your Summoner Icon and unlock automatically as your account reaches specific levels. There are currently 21 League of Legends level borders, beginning with Piltover at level 1 and ending with Eternus at level 500. Once you unlock a border, you can select it again at any time instead of being forced to use your highest-level option.
Riot has not added any new level borders, with Eternus remaining the highest available border at level 500. Your account can continue leveling beyond that, but you won’t get anything new. However, in the past, Riot has added some of the borders retroactively, and as the playerbase’s overall account levels rise, there’s a chance the devs will add more borders for levels 500+.