How to achieve a flat rendering with translucency and shadows?

I’m currently working on a mobile project where I’d like to achieve a flat cel-shading style rendering while preserving both translucency and shadows. I attempted to use a post-process for cel shading that gives me shadows; however, I’m losing translucency in the final render.
What options are available to achieve a rendering similar to the one shown in these references?

Aquarium Land


Season : A letter to the futur

Thank you in advance.

There are plenty of “cel shading” tutorials and plugins on the marketplace.

Look at one of these perhaps:
Ultimate Cel Shader in Materials - UE Marketplace (unrealengine.com)
Cel Shading and Outline by Raio in Materials - UE Marketplace (unrealengine.com)

Even if you want your own in the end, buying one of these to pick it apart and learn how they did it seems like an affordable class!