I say 'cure' in quotes since, depending on the disability and the context, it may not even have a cure or it's less of a cure, more a very helpful accomodation... and sometimes the cure is more of a curse in disguise. Bonus tragedy if they could've gotten the 'cure' without villainy.
Otto Octavius in Marvel's Spider-Man (2018):
May be the poster boy for this trope. Otto suffers from a neuro-degenerative disease that threatens to render his entire organic body immobile, so he works on making artificial limbs he could use to live when his mobility is taken away. The 'tentacles' are connected to him through a nerves interface, and has the side effect of bringing out the worst in him when he uses them for too long... although it's less the tentacles turning him villainous, and more bringing out what was already there, i.e his visceral hatred for Norman Osborn. When Norman screws him over again, putting his 'tentacle research' in danger, he snaps and turns into a complete villain. At the very end of the game after his defeat, Otto begs and screams for mercy... because they're going to take away 'his arms' in prison.
Walter Skykes in Warehouse 13:
(I haven't watched the show in forever so feel free to correct me if I make a mistake) Walter was bound to a wheelchair ever since his childhood, until he came across Carlo Collodi's (the guy who wrote Pinochio) Bracelet, an artefact that gives its wearer extraordinary control and strength of their body, letting Walter walk again. But like pretty much any artefact in the series, it has a heavy price: Wear it long enough, and it will rob its user of their ability to give and recieve love, as well as an addiction to the bracelet itself. When the Warehouse staff learned of the bracelet, and that it was in possession of a child, they took it away from Walter... but it was too late. Walter couldn't go back to his life wheelchair bound, he was vengeful towards the staff and desperate to get the bracelet back, resulting in his villainy. For bonus tragedy, during his grand finale, an artefact that brings 'peace' was used on him to attempt to stop him from blowing up the Warehouse... and it worked, negating the dark effects the bracelet had instilled in him, leaving Walter horrified at what he's become. He disables the bomb and apologizes before dying of his injuries.
I also want to mention Muzan from Demon Sayer, who wants to be able to walk in the sun... but he's not tragic, he was a complete POS from beggining to end. His death/defeat isn't sad, it's cathartic.