I don’t really have any hard statistics about attrition rates of students. I imagine that it is pretty high for people starting curricula like this - you get a lot of people with superficial enthusiasm or who think this will be easy and quick. But I imagine it improves as time goes by.
But FCC is a good path. It leaves you with some great frontend knowledge, gets you familiar with some important libraries, and gets you going on some backend stuff. Is it enough to make you a web developer? That’s debatable. But at least it gets you a good solid foundation and the knowledge to see what you need to work on next. And there are people that have landed great jobs after getting the FCC certificates. I just wouldn’t count on it as a fait accompli.
Just put in the work and learn. Learn to love coding and learn to love learning. If you do that, the job will (eventually) find you.