Update 2.1 was the eleventh official update and arguably the most influential in the game's history. It introduced a massive amount of content that defined the "modern" look of Geometry Dash levels:
New triggers, dash rings, custom gameplay rings, and red speed portals. Why Use a v2.1 Repack? geometry dash v21 repack
Input specific download commands (found on sites like SteamDB) to pull the 2.1 files. Update 2
A teleportation-based movement style that allows players to instantly switch gravity. custom gameplay rings