I recommend you slice the solid into three parts. Only the center part needs to be Flexible.

The lid and base don't need to be included in the bending of the plastic hinge.

This much smaller solid body should be meshed with much smaller elements.

You need at least 4 elements through the thickness. If you slice the uniform cross-section of the hinge, you can use Method = Sweep and put 8 elements through the thickness while using Hex elements.

Add Plasticity to the material model. For example, Bilinear Kinematic Hardening where you enter the Yield Strength and Tangent Modulus. A simple way to model plasticity is "perfectly plastic" which means the Tangent Modulus = 0.