For me Genshin Impact and Hades (including Hades II) are two examples. These games have relatively simple art styles in comparison to e.g. the realistically painted art of certain Blizzard games (WoW, Hearthstone hero portraits), but they are hard to learn even to someone more advanced in art creation.
Probably Enter the Gungeon, since it’s actually rendered in 3D even though it has a 2D presentation.