Ask an Immigration Solicitor. Get an Answer ASAP.
I am a UK solicitor.
What would you wish to do in the UK and how long do you intend to be in the UK for?
I am afraid I do not see a relevant category for a UK work visa for someone like you who wishes to come to the UK indefinitely to work as a screenwriter/creative field.
You would require sponsorship by a UK employer in order for you to be eligible for a UK work visa.
May I help further?
I am afraid you would need a UK employer to sponsor you unless you have a UK family member eligible to sponsor you e.g a partner.
If you have £2m or equivalent, you may apply for an investor visa which does not require any sponsorship: https://www.gov.uk/tier-1-investor
All the best