Mask a MeshRenderer

Hello! I have a moving MeshRenderer (a Plane). I need to hide it / not show it as soon as it enters a certain region of space in the game, delimited by a curved line. I only need to hide the portion of the mesh that enters the region, I cannot disable the entire GameObject.

To make things more interesting, there are other objects that can cross the same curved line but need to remain visible.

I have tried experimenting a little with ZBuffer and Stencil concepts but I am completely stuck now.

Thanks for your help!