I don't know much about Sinon. I have never run a game there - although I played some Oriental Adventures years ago …

We know that …

• Way and Shan (deities, temple of the Shrines) came from Sinon (It is in their backstories)
• The Shay dynasty of Porters bar came from Sinon - generations ago

But I think that is about it for established in-world Lore.