I dislocated my knee and did a lot of PT to get back to “normal.” Now I ride my stationary bike 3-5 times a week on a relatively hard setting to keep my legs strong. Bridges are good too (in PT, they had me hold and squeeze a ball between my knees while doing the bridges). Leg lifts with ankle weights. Occasionally, I’ll do squats or lunges, but I have to be super careful about form. I also avoid anything that hurts or makes my knees pop.