Niche: follow my passion or my expertise

I’m a certified executive coach, and I believe I have the tools to offer also life coaching (thanks to my certification and to scholars).
I work 4 days per week for a company as an organization and teams coach, and I like this job.
I also like writing literature, and finished a book that is not accepted by editors yet.

I’m about to launch my one-on-one coaching business, which is what I prefer. I’m going to start by working one day per week on my business, and keep my job 4 days per week.

I’m hesitating between two offers regarding the niche for my business:
1- Offer : A coaching process that helps you finish writing the book that you dream about but have not been able to finish
=> Niche = beginner writers.
Writing is my passion, but I don’t have deep expertise, so I cannot give advice for example about how to write a good plot. However, I can help for the mindset, motivation, how to overcome failures… which is I believe the most important part.

2- Offer : A coaching process that helps you show up as the best version of yourself at work and achieve your ambition
=> Niche = managers.
For this domain I have the expertise so I feel more confident. But I’m afraid that if I start marketing this business on LinkedIn, my current managers at work will find it unfair that I start my business in an area that is close to my current job, instead of offering it with the company.

I would like to have your opinion!
Thank you very much.