It depends on what you mean by professional writer. Being a developer advocate, at many companies, is equivalent to writing full-time, and a software engineer w

It depends on what you mean by professional writer. Being a developer advocate, at many companies, is equivalent to writing full-time, and a software engineer who has recently developed an interest in writing is typically an easier sell for those roles than a writer who has recently developed an interest in code. This is basically true for all domain-specific writing jobs as well. Being an expert in the domain and being interested in writing is in many ways advantageous compared to being an expert in writing with an interest in the domain.