Thank you for sharing your experience. The available cartilage can adapt but research doesn't show regeneration through exercise alone. Some medical treatments (types of injections and sugical implants) show promise but that is outside of my scope. Loss of cartilage does not guarentee a future of pain and no function. The severity plays a role along with your overall health status (metabolic health, muscle mass, bones health, weight, etc.)

With stairs being a primary issue, I recommend focusing on developing quad and gluteal strength. If a personalized and long-duration exercise program does not help, a TKR may be a good option. I recommend talking with a few physicians. Even if you go the surgical route, prehab will be a large beenfit. Are you able to do open chain exercises (knee extension leg curl)?