When you create a homebrew world, there are nearly infinite details that you can develop. There are of course the obvious ones: the basics of the setting, its historical context, its natural world, the fundamentals of its political world. But there's so much more than that. I think the impulse with homebrew settings is to find ways to adapt modern and historical fact into the fiction of the world, and there's nothing wrong with this. I myself use those kinds of details to characterize a few of my takes on classic D&D groups. My two human groups are pretty directly based on real-life history--the Daltoners are western European in inspiration, specifically a caricatured version of the British Empire, and the Faninites tend to draw from Viking culture, though they're explicitly a lot more peaceful than classic Vikings. Similarly, dwarves are a mixture of Germanic tribes and Roman civilization, and elven society is loosely based on feudal Japanese culture. That lets me keep a pretty traditional high fantasy aesthetic to a lot of the world.
But other elements can take whatever direction you like. My gnomes are technologically-focused as classic D&D calls for, but my take casts them as strictly socialistic and free-thinking; my halflings are anarchistic and focused on nature preservation; my orcs are tribal but also highly spiritual with some borrowings from Egyptian culture, making them a pretty unique mixture of ideas that resists classic D&D characterization--my orcs hold up war as a culturally important thing but prize peace and mutual support in ways that runs counter to most tabletop depictions of them. In a similar way, choosing atypical things to develop in a homebrew setting can set your world apart from the standard depictions of settings. That's why I've chosen idiosyncratic (but still relevant) details to spend time thinking about. A few of the more distinct things I've chosen to characterize are specific societal and cultural aspects of my groups, things like senses of humor, conspiracy theories, parenting styles, and funeral rites.
Details like these may seem trivial at first, but I assure you that there's more to them than meets the eye. Most tabletop game have NPCs that are meant as comic relief, and having distinct senses of humor between cultural groups means a more intricate and diverse approach to those humorous characters. Conspiracy theories tell us about the truth of the world and its misconceptions, which tell us about the ways that people in the homebrew setting interpret the world around them. Parenting styles can define the childhood, adolescence, and adulthood experiences of people, and seeing the ways that different groups define those roles can help to set apart people from different cultural backgrounds in surprising ways. Funeral rites can be an important detail in that death is usually a fairly omnipresent factor in tabletop games, and how people celebrate life and death tells us about their beliefs about the world in addition to really spicing up scenes that involve the loss of a player character or NPC. So with that perspective in mind, let's approach romantic and sexual relationships, which can hold a similarly important role in the ways that different characters get along in the reality of the game.