Can I create a fintech application? how to do it?

I have installed several mobile banking applications and surely you too, but I have always had the question, how do you do it? does anyone have any idea? and the question that matters most to me is, can someone like me create their own financial application? Since they are bank applications I usually think that only people with a lot of money can create them, for example businessmen, but can people or common users like me create it?