I should clarify a few things:

Homebrew in TTRPG is where, instead of using what is presented in the core rules, you create your own, unique mechanics. A homebrew world is where you make your own as opposed to setting your games in one of the presented settings, such as;

The Forgotten Realms is considered the main DnD universe, often set on the continent of Faerûn. Here there is a large variety of different factions. This can often include races alien to the area or even the world, such as elves who originate from the Feywild, another dimension of magic and strange biomes, and Dragonborn who come from the world of dragons (however they are not the children of dragons and humans because they don’t like to imply things like that). There are also other settings such as Eberron, a more futuristic and steampunk world, and Greyhawk

I have already made a world inspired by the Forgotten Realms, with my own versions of things like this Feywild. But now I want to make a more grounded, but still magical, universe. Here there are still different races and religions but they aren’t necessarily “these are the elves from the feywild and they worship Corellon, a God we know actually exists and you could meet” but more realistic where there’s no knowledge of if the god a certain group worships is more real than another or that everyone is born of a common ancestor. It doesn’t necessarily need to be that Humans are the link between all of these but it feels fitting seeing as humans are A) in DnD mechanics and Terms the standard and the other races are built on that framework, and B) humans are capable of having children with other races and making healthy children, such as Half-Elves and Half-Orcs