There are so many white papers available on the AWS official site , not sure which white papers to download for my AWS Solution Architect Professional exam .
There is no easy answer here. You can try to read all of them but that’s a lot. There is no specific list of whitepapers and exam questions can come from any and all of them. What you will find is LOTS of overlap in the various whitepapers…meaning they will say the same things. As you read them, you will see this and you can start skipping over instances of this that you already know and have read.
Your strategy should probably be to feel confident enough to know at least 80% of the material…it’s rare that someone masters 100% of the things.