[kingu]

Treemale is pretty easy to spot out there. The 8 under the x could easily be 18, or more likely, 8 with the x marking the spot. The three math lines are telling a substitution code that’s likely the next close.

The ship+arm and sunset... It’s also possible that shiparm would mean something different with a substitution code.

Me, I’d dig 8 paces west of the treemail and likely find the hidden immunity idol.

[cuz_it_aint_their_money]

My guess:
"X" + "Cave" + "8" = excavate
If "E=V" and "J=X" then "H=W" (the 23rd letter)
The arrow is pointing to the "yardarm" of the ship, therefore "Yardarm - arm" = Yard
The sun is setting in the west (and they are on the west coast of Nicaragua)
The last picture is a mangrove tree
Therefore...
Excavate 23 yards west of the Mangrove tree.

But like I said, it's just a guess.