Is it true emergency contraceptive pills do not work after ovulation? do they have any effect on thinning the lining of the uterus to prevent implantation?

Plan B acts primarily by stopping the release of an egg from the ovary. It may prevent a sperm from fertilizing the egg. If fertilization does occur, Plan B One-Step may prevent a fertilized egg from attaching to the womb. If a fertilized egg is implanted prior to taking Plan B One-Step, the drug will not work. ref: https://www.webmd.com/sex/birth-control/features/plan-b-11-questions-11-answers