I have had problems with my knees for some years. I take glucosamine which is said to help with arthritis. I do gentle strengthening exercises daily.
Gentle squats, stand holding on to something and then squat slightly as if you are going to sit down, and then straighten up. I have 2 kilo weights which I strap on my ankles and straighten my legs while seated, also something called a glutes bridge, laying down with knees bent and raising your bottom, just for a second or two and then lowering ( though it's not always easy to get up of the floor after). I do 15 repeats for each exercise. These exercises were recommended by a physiotherapist.