Best quad-strengthening exercises?

So, I’ve got a question. I know people have posted stuff like this before, but I haven't found exactly what I'm looking for.
Last year, back in February, my kneecap popped out of place—patellar dislocation with spontaneous reduction. Wasn't even the first time, either. Ended up in the ER, stuck in a brace for two weeks, and then had to get a joint aspiration to drain about 70ml of fluid... After that, I started physical therapy. So far, I've done five rounds of ten sessions each (exercises, electrical stimulation, laser, magnets, all that), but my quad still feels pretty weak.
Last year, my left leg was about 4 cm smaller than my right. Now the difference is down to 1 cm, but I figure it'll catch up once I get stronger. I'm mainly looking for specific quad exercises or just general advice on what helps with knee stability.
I know swimming and cycling are good, and I'm thinking about hitting up a local gym.
Thanks for any help 🙂

In my estimation, you really ought to steer clear of traditional squats altogether; or, if you simply insist on performing them, you must ensure you aren't engaging in a full range of motion. Generally speaking, any exercise that forces the angle between your femur and your shin to drop below ninety degrees is off-limits for you. If you have the luxury of a gym membership, that leg extension machine is an excellent tool to utilize. Alternatively, if the idea of a gym doesn't appeal to you, experimenting with resistance bands serves as a perfectly viable solution.

Yeah, I don't do any core work. And swimming? Breaststroke is off the table because of some weird knee angle issue
I was planning on hitting the gym tomorrow anyway, just looking for some ideas

Hey, quick question!
I have a displaced right kneecap and I've been doing these quad-strengthening exercises...
Is it normal for my knee to sting from those moves? Like, just right at the tip of the patella? I worked out with a 1lb weight last night and it's been stinging ever since. Maybe it's because it was my first time using any weight at all.

Look, I’m no doctor, but if I were you, I’d ditch the weights and just move freely for a while—especially since this happened so recently. Your ligaments are probably still pretty fragile, and that nagging pain is likely just them telling you to slow down.
That was my experience, anyway.
As far as exercises go, the elliptical trainer at the gym was my absolute lifesaver. I’d pair that with some resistance band work and maybe a tiny 2-pound weight here and there. Mostly, I just stuck to the stuff my physical therapist at the Mayo Clinic showed me, mixed in with a few things I made up on the fly.
Eventually, I graduated to the knee machines—you know, those ones where you push your legs out or pull them in, and the standard seated or lying leg extensions.
Whatever you do, stay away from squats, especially if you're trying to add extra weight. That’s basically a death sentence for your knees 🙂 .

That’s all I’ve got.