Can you name all landmasses with an International Border?
Overseas territories are included, but not heavily disputed ones such as ones in Antarctica.
It must be the largest landmass with the border between those two countries. So for example, Chile and Argentina have a border on Tierra del Fuego, but because they also have a border on a larger landmass Tierra del Fuego is not included.
Not counting artificial islands or very small islands in causeways
If it exists that means that Sri Lanka is actually just a part of the Afro-Eurasia landmass. Then it would come under Afro-Eurasia. Alternative definitions may put some sort of border in the "very small islands" category.
You've missed a couple. Tierra del Fuego (full name Isla Grande de TdF) and the Baltic island of Usedom, whose border I crossed last year (Germany-Poland).