I received a biodegradable plastic cup with my meal once.
When we returned home, we put it in the composter so it could bio degrade.
It then spent years cycling through the composter. Every time it came out the back end we’d stick it back in the front to cycle through again in hopes it would bio degrade. It did not. It was as pristine when we gave up the endeavor and threw it in the garbage as it had been at the beginning.