While a true 1.21 Eaglercraft client isn't fully realized, there are workarounds:
The community is actively working on "Eaglercraft 1.19" and "1.20" projects, which will pave the way for 1.21. For now, the best experience remains , which offers the best performance and the largest player base. eaglercraft 1.21
Most developers in the community are currently working on a 1.20 or 1.19 port first. Jumping straight to 1.21 is unlikely until the foundation for modern rendering (like the 1.13+ engine changes) is fully established in the browser. How to Play "Modern" Minecraft in Your Browser Now While a true 1
I will provide an article focused on the and the community's progress toward modern versions like 1.21 , as that is the most likely intent. Jumping straight to 1
The gold standard for performance and multiplayer. Eaglercraft 1.5.2: A nostalgic version for older hardware. The 1.21 Hype: What’s New?