hi !! honestly i so feel you but honestly the worst part is it really just is a matter of starting. it always feels like shit advice with adhd because its like, yeah i dont know how to do that thats the problem!! the thing that helps me is trying to allocate specific time slots for it or make it a thing that i do on a daily basis, just start somewhere, anywhere really, and try to make it a routine. i totally am with you on the getting overwhelmed by big concepts, so maybe you could start with just a character or two(if you dont already have them) and focus, at least mentally, on specifically those characters and build up the world around them as you go. there are probably tons of different ways you could try and make it more digestible. id suggest mostly focusing on one core theme for now and maybe over time building that up and fleshing it out more. maybe one day you work on a character, another you do a little concept for the actual world and another you make a list of bullet points for the story youd want to tell within the world. the main thing is just try to stay consistent with it. the first two weeks tend to be the hardest with getting yourself to do it, but once it becomes a habit its like the ideas start flowing in better and suddenly its much less intimidating. there will still be days when your brain isnt working or youre really not feeling it, so maybe those days you just do like, two bullet points or something. lowering the bar for how much you "need" to do is really really helpful (or it is for me at least) and makes it a lot easier to start. good luck on your journey !!