Big Globe is, at its core, a Fabric worldgen mod that overhauls all 3 vanilla dimensions and makes them much bigger. The overworld is 2048 blocks tall, while the nether and the end are both 1024 blocks tall, so yeah, there is a lot more room to build, explore, and get lost in.
It is not just about taller worlds either. Big Globe adds custom terrain features everywhere, plus over 100 new blocks that fit in with vanilla or add a few handy mechanics of their own. A lot of the content is meant to feel natural and decorative, but some blocks also make certain parts of the game easier or smoother to play.
Big Globe also includes its own scripting language for datapacks, which can be used to create worldgen features with custom rules. Most of the terrain generation in this mod is built from those scripts. Just keep in mind that most normal worldgen from other mods or datapacks will not affect Big Globe worlds unless it is made to work with it.
To join, you need the Big Globe mod for the exact same Minecraft version as the server. Use Fabric and add the mod to your launcher setup, then you are good to go. Builderboy's choice!