Worldbuilding sounds intense and I think it is.... how to start. I think it's the setting... it can be anywhere. I chose the World of Pteros it is my oldest title and housed on Youtube. I created this as intro to my future content and here are the steps I took were as follows:
Chat GBT: prompts
Midjourney
Kling 2.5 Turbo (Kling Acct)
Suno
Adobe After Effects
Youtube
The challenge for you is to start thinking about a home for your future characters, what kind of world is it? Don't fall down a rabbit hole of what about this or that. First thing that sparks you imagination. Do it. One still and post here. Once we are at that point we will move to the next. I call every step a FACET. And my personal rule is simple, one facet at a time.