Thanks James, I don't have too much information yet because I have not give an offer and had inspection ppl come to check.
But it does seem very similar to the post you shared, and I live in an area with lots of ground settlement. It does look like the pool is sinking.
And the house is on the direction of the crack and is also very close to pool (very narrow back yard). so the foundation of the entire house is likely affected by this.
The old owner rarely lived in this property (a rich foreigner who does not even live in the country) and never minded to update or check anything.
So I guess the owner does not know anything, and no regular maintenance ppl to talk to. But the builder is local, I may be able to contact them.
The pool was installed 15 years ago
I may have to pass on this house, because I wouldn't have 40 grand to fix it after paying for the downpayment and moving. and also the house foundation could be a larger problem... Anyways, Thank you so much! I am so glad I came and asked before getting in a huge trouble. Thanks again!