Definitely Croatia but unsure if it's Hvar. Really dredging through the memory banks, but I think it might be the area around here? https://maps.app.goo.gl/7oYVDnGXF3fD24s17 It's one of the lines featured in Depth Charge
Checked Depth Charge and it's definitely Kornati. Big area though and not sure exactly where they ended up climbing.
Doesn't narrow it down much, but there's a shot of a map at the start of the film where they indicate it's roughly this kinda area.

Ooh nice one! Uninhabited island with rocky cliffs sounds ideal.