I am a senior living with a relative. Is there any way they can force me to live in a facility if I am of sound mind?

If you are of sound mind you can move wherever you want. Nobody can ever make you go to assisted living or a nursing home if you are of sound mind. My 95 year old mother is living proof of that. She lives by herself in her own home.

It’s not a plan to assume you can even partially live on a book you wrote. Has it been published? Do you have an advance from a publisher? Or is it a book you’re hoping will sell?

JK Rowling, the famous (and rich!) Harry Potter author, was rejected by 12 publishers. It took over two years for her to get a publisher, and it did not sell big right away.

It’s fine if you want to be on your own again but you must have a job, with a steady income, in place to survive. Hope and assumption won’t pay the bills.

If you are living with a relative they can certainly ask you to move out. No one can force you into care if you are not in danger. But are you sure that a more supported living environment wouldn't be a good idea?

There are so many levels of senior housing. There are apartment buildings for completely independent older people. They have apartments with full kitchens. Then, there are places where you still have your own apartment but they may only have a sink, microwave and fridge and have more services, like meals or a bus that takes you to the store or doctor. Maybe that would be a better plan for the future? You might be completely independent now, but it would be good to have services available if you need them in the future, wouldn't it?

Call the Office for Aging for your state. They can help you.
https://www.hhs.gov/programs/social-services/programs-for-seniors/index.html

You can do whatever you want unless the courts deem you unable to . Just take off and don’t come back.

If you are of sound mind you can of course move wherever you like, and wherever you can afford to move.