To help stimulate our dog when she was older, I got a kiddie pool and a several packs of plastic balls, like for a kid’s ball pit. Than hid treats in the pit for her to search. She loved it and it would keep her entertained even after all the snacks were found.
Have you talked to a medical malpractice lawyer about your original diagnosis? Most will do an initial consult for free and work on contingency. In this rock-paper-scissor world lawyer beats doctor.