I wonder if anyone ever looked for it?
And Spain would undoubtedly try to claim it but since rather then losing it they threw it away would they have any case?
It’s probably a myth.
It took arsenic (which was something the sculptors needed to avoid inhaling) to make the platinum metals (I think there are four, usually found together) workable for metalsmiths, beginning in the 18th century.
https://www.metmuseum.org/art/collection/search/205701
‘Back in the 1500 Spain dumped tons of platinum in the ocean because they thought it was worthless ‘
Lots of people claim to have had boating accidents