You cannot join standard Minecraft Java servers directly using an Eaglercraft client because of the TCP vs. WebSocket barrier. However, the community has built bridges.
Here are some key features of Minecraft 1.8.8 Eaglercraft: minecraft 188 eaglercraft
Eaglercraft 1.8.8 has become particularly popular for multiplayer gameplay, especially for PvP (player-versus-player) combat. The version is favored by many because it features the classic, simpler PvP combat system (click-based) that many players prefer for competitive multiplayer, before the combat overhaul introduced in version 1.9. You cannot join standard Minecraft Java servers directly
You might wonder: Why not 1.16 or 1.20? The answer is technical limitation and community preference. minecraft 188 eaglercraft