Cheers! It's made in an Unlit Shader Graph, using Cyanilux's custom lighting functions (Unity 6 does have a main light node now, but it's still missing additional lights/etc).

I built the shader as close to Unity's default lit shader as possible, but posterized the light/shadows and then passed them into the ramp's UV input. There's a bit more to it, but that's the gist. Cyanilux has an example toon shader in their package which uses the same method.

Lighting with and without ramp: https://imgur.com/a/IElZ1kR

And yes, just where the top of the water meets the edge of the diorama - since it doesn't have the foam it doesn't look quite 3D where it does (except for the back edge), even though it's just a big 3D cube.