Look into glute and core training to stabilize your body. When you have strong glutes and you're walking/doing any activity, your body will be more stable and put force away from the knee. Most knee/hip injuries are because of weak glutes. Now again, I am not 100% sure what 'osteoarthritis' is, but I've helped many people away from knee injuries by applying these techniques. Might be worth looking into for you.
For weight loss, you don't need to do any exercising if you don't want to. You also don't have to restrict yourself from any type of food if you don't want to (stuff like keto is pointless). The only thing that matters is being in a caloric deficit to lose weight. Stuff like 'stop eating meat' is bullshit.
So you claim 'stuff like stop eating meat is bullshit' here even though you've admitted you have no idea what osteoarthritis even is. Don't get triggered and your emotional and block-headed political standing on meat--eating get in the way of objectivity here. Mindless, brash, futile comments like this have no place here when we're talking about helping someone with a very distressing illness.
Speaking objectively, it's essentially a degenerative disease effecting joints anywhere in the body. Left untreated it can spread to other parts of the body, which tells you what?.... it tells you that it's due to imbalance in (actually quite simple) biochemical processes. As a result, the body is unable to cope with inflammation caused, resulting in the condition. This is nothing like tying to nurse someone with a torn ligament. This is a biochemical problem, not a physiological one.
Your broscience cliches are actually very dangerous. Telling people you can lose weight with a simple caloric deficit is easy and all well and good, but what will happen when someone all ready burdened with chronic ph imbalance are potentially made worse.... sure you will lose weight on a simple caloric deificit, but then it becomes a little more complicated than that....
in this case your body will begin to mobilise fat to use for energy which means a dire surge in fatty acids being carried to all tissue around the body including you guessed it, to joints already afflicted with severe inflammation, making them worse. And what happens then.... when you're adding insult to injury by eating 'foods', meat, eggs, sugar, starch, salt which invariably produce acidity. It sounds like a recipe for disaster doesn't it? That's because it is. You might lost some weight but you'll be damaging your joint further too if your kind of advice is followed, to a person already suffering from a severe ph imbalance.