Is there any single word for a writer who is new to writing?
A "novice" in any field is someone who is new to it and inexperienced. There are plenty of synonyms - beginner, or trainee, for example. If there is a specific term for a novice writer, I'm not aware of it, but all these words imply that someone is new to the entire concept of writing professionally
However, an author who is publishing their debut novel may be a "new" writer to their audience, yet they may have perfected their craft before getting to the publishing stage. Calling a published writer a "novice" might not be right in this situation. A better word might be "newcomer", which indicates that they are new to publishing, but not necessarily new to writing.