This is just Session 0 connection to homebrew for me. Interesting on how it connects, but not relevant unless you run a homebrew AND your session 0 is a big influence on it.
Actually, my homebrewing is heavily involved in Session 0, let me post that next because of how intertwined they are for me.
Worldbuilding for me is in a bunch of phases. Here's a "standard" campaign, though it can (and always does) vary based on other aspects, like I'm currently running a frontier/exploration game that definitely modified this.
First phase is very broad strokes, view from 50K feet sort of thing. What I want is things made of plot hooks and awesome. I want players to hear about this without being overwhelmed, and be able to go "I want my character to be from there" or "I want to adventure there". Details are my enemy at this stage.
Then session 0 with the players. Where we discuss the world, what they are interested in, and make characters. I give my players a lot of narrative control around their characters and other things. One player wanted an order of knights that guarded these netherportals where you left behind you old life to join. Easy. Another, a druid, wanted the moon to be the skull of a decapitated god and the land to be their body, so that druidic magic literally was a connection with the divine flesh. A little bit of thought if this interfered with anything else, and then sure, why not. Player buy-in on ideas they come up with is very high.
This gives me big vision ideas about the direction the campaign can go.
From there I will have an idea of the group and how (/if) they know each other, so I can figure out where they are starting. I flesh out the area, adding some details on a moderate-big scale, then more on a smaller scale, and so forth until I have a well fleshed out starting area.
As part of that I'm thinking about what types of questions the uniqueness of this setting is good to answer, stories that fit better here then a generic world, especially giving the nature of our protagonists. I start to work out some ideas for those stories, but really just ideas into "Act II" - none of it is true until it hits the table, but I do want things I can foreshadow and have reasons for why.
So then I work out some starting adventures, flesh out the world for what I need for those, and work out some character arcs to weave in around everything else which also often requires making organizations, understanding politics and tensions, and otherwise adding details to the world.
Then, as the group adventures I pay attention to what the players seem most interested in. I make sure to seed that liberally into adventures, and further flesh out the world both to deal with their explorations and travel as well as to support stories about their goals and to further their character arcs.
In the end, I may have parts of the world untouched, and others crafted in loving detail. But it really happens over the course of campaign, directed by player interest, character actions, and the consequences of them.