Currently, standard Eaglercraft builds cap out at mechanics (with 1.8.8 PvP being the most common). Because Eaglercraft is a reverse-engineered project (not an official Mojang product), updating to 1.21.1 is a massive technical hurdle.
However, if you are looking to play the standard , or if you are looking for the actual Minecraft 1.21 experience, here are the guides for both. eaglercraft 1.21 1
Eaglercraft is a decompiled version of Minecraft (specifically based on the Java Edition) that has been ported to run on JavaScript and HTML5. Because it runs in a web browser, it bypasses the need for a high-end PC or a dedicated game installation. Currently, standard Eaglercraft builds cap out at mechanics
Eaglercraft 1.21.1 is an ambitious community-driven port that attempts to bring the modern Minecraft "Tricky Trials" experience directly to web browsers using TeaVM technology. here are the guides for both.