In which category of Graphic design I can get order quickly?
Go with whichever you enjoy the most and feel the most comfortable doing.
This is not a get rich quick scheme.
you do your best in any category of design then you will achieve your goals
I suggest that you explore the graphic design category in detail yourself - you’ll find that there are thousands of sellers offering various forms of it.
If you can find something that is in demand but has low competition - and that you actually have the skills to offer! - then go for it.