The problem here is something else. It is not about how to show (single step or multiple steps).
It depends on what information you are asking.
There are two origins of informations. One is stored in user's mind and other is out of their mind. Obviously, they feel easy and quick to express right from their mind.
Let me create an example. You are asked to fill your passport no.(8 digit) and mobile no. (10 digit). Which is less headache? huh?
You got it right?
Now let's focus on its presentation aspect. I don't see much problem to ask informations like mobile no. in multiple steps. Sure it'll be more user friendly than one long scroll. Now you might be thinking how to ask information that is NOT stored in user's mind like tax ID.
No user feel better at 3rd step (after login) asking tax ID. They wish they could have been informed before. If the tax document was not nearby, they wouldn't have started filling the form.
Make sense right?
Now it is upto you to decide what is best for your app.