The schools are really specific on who exactly can be a reference letter writer for you. Sometimes even a specific as a professor in the program you majored in while others say a professor. You really want to find people who can write you great letters of recommendation and not someone who knows you very well, it’s a common misconception those things are correlated. Often times managers, professors, and other people you’ve worked with and worked for Who you may not feel like you know well are very aware of the value you offer because they have seen your skills in action.
When you ask for a letter of recommendation explicitly ask the source if they can write you a great letter and if they don’t give you an answer that’s clear or you don’t feel good about it don’t have them write you a letter because it may be worse for your chances of being excepted.