The real world is very complex and connected, yet we still construct narratives around and about it. The choice is not necessarily to simplify the world, but to ignore 99% of it when focussing on a good story. It should be just fine to create a complex and interconnected world.
Separate your Worldbuilding from your Narrative efforts. The world description should be broad, with lots of idea leads, and the story content should be deeper, full of detail and references that place it in the world and flesh those ideas out.
When Worldbuilding, define things broadly and loosely, so that you are not constrained later when ad-libbing or filling in Narrative detail. Expect to only use 10% of what you prepare. You need to be OK with having a great idea for a character or place, and to never see that getting more than a mention. The way to keep it simple is to focus on breadth first, short, open descriptions, and to avoid filling in detail out of sense of completeness.
One way to approach breadth-first descriptions is to "just write the whole thing" quickly and crudely, then go back and re-do with slightly more detail. Repeat until you run out of time for the current worldbuilding stage. Your first attempt might be no more than a paragraph about the whole world and the kind of beings that live there. Then a second pass might mention the largest units of culture - e.g. countries. Then a third pass might name the rulers and pick out one or two interesting facts about each country/area. Doing it this way forces you away from filling in exciting narrative-based details until you are ready. It also makes you think about whether you are currently working towards a world description or a story set in the world.
When gaming, or writing a story, make decisions improvised around the breadth of your world-building, and focus on:
a) At the start of the narrative, open up possibilities. Add interesting new details and make decisions which drive the nature of the remaining plot. This is a good time to decide on what will link to other things in your story. That's not to say that everything else is not linked, just that not all links need to be active complications for every tale. You ignore the evil henchmen's family connections if it just drags more characters in without satisfying the story's goals. Invent a (reversible) reason there and then why it is not important this time, if that helps.
b) In the middle of the narrative, have the simplest, most obvious things happen, and avoid opening up new possibilities. That doesn't mean avoiding new characters and things happen as far as readers or players are concerned - but those things should ideally be obvious to someone with your whole-world view. I suspect that you may be doing this too late currently, leaving yourself not enough time to deal with consequences, and in essence trying to create a tale that is 50% start and 50% end, when the split might better be 25% / 50% / 25% beginning, middle, end.
c) From the middle to the end of the narrative, seek closure and rounding off of loose ends.
Do all of the above using broad knowledge of the world that you sketched out. To your readers or players, the information about the rest of the world is not already available, so ideally they will not notice the changes of behaviour you use from a) to c), and just get to enjoy the story unfolding. The fact that the world has far more depth than the protagonists get to interact with should hopefully come across in your confidence when improvising.