If you are waiting for 2.21, here is what you can realistically expect based on teasers and datamines:
For the most accurate and up-to-date information on Geometry Dash updates, including any potential 2.2 or 2.21 releases, I recommend: when is geometry dash 2.21
Geometry Dash was first released on August 13, 2013, as a free-to-play game on mobile devices. The game's unique blend of rhythm-based gameplay, colorful graphics, and challenging levels quickly gained it a massive following. Over the years, the game has received several major updates, including Geometry Dash 1.5, 1.6, 1.7, and 1.8, each adding new features, levels, and game modes. If you are waiting for 2
This is the big one. It will allow players to compete against each other in real-time. While it won't be a "collision" based multiplayer (you won't hit other players), you will see their progress icons as you race to the finish. This is the big one