Following the takedown of the original project, the Eaglercraft community fractured. While several community forks have attempted to modernize the client, progress toward 1.20 has been limited:
Crucially, Eaglercraft is not an emulator or a remote desktop stream. It compiles a modified version of the Minecraft Java client to WebAssembly and JavaScript, running the game logic natively in your browser’s sandbox. eaglercraft java 1.20