What is the 4" white pvc pipe in Pool patio concrete slab?
Probably a place to insert a umbrella pole
It's randomly located so likely not a drain. Any water that near the pool would likely drain into the pool.
Edited to add this picture as an example of one, and a link to the seller
https://www.poolsupplyunlimited.com/pool/aquastar-us105-umbrella-stands/5841p1