Knees never really go back to 100%, best you can do is build muscle around it to reduce the chance it blows out again.

My knees have been kinda fucked since I was a teen because of some genetic bullshit. I never really injured them proper, but it's been at a point where I could barely walk stairs without severe pain, even when I was young enough to be invulnerable.

I was like 30 when I finally stopped being a fucking idiot and started taking my shit seriously enough to do something about it. It took maybe a couple of years of strength training (1x a week for the first year, then 2-3x a week, lots of front & back squats, knee extensions, romanian deadlifts & other deadlift variations, etc) to build enough muscle to almost entirely get rid of the knee pain in my daily life. My knees are probably still kind of fucked underneath all the muscle, can't really do anything to actually "fix" them at this point. I just gotta make sure to keep going to the gym.

No I don't think anyone ever has. In my experience, every person that had a knee injury eventually dies.

Physical therapy helps a lot

Walking daily and losing a lot of weight.

From a basic running injury type thing? If so, technically, but it basically took a full year. Knees are finnicky things, probably owing to how much we use them on the daily.

I went running once and tore something in my knee to where I couldn't really walk right (but did stupidly anyways) and couldn't climb stairs anymore. I pushed through and it did get better, and then I had to slowly start running again. After a year or 2 I stopped having any major issue with it

I didn't stretch almost every day while it was injured though, with whatever stretches didn't hurt. Not a medical professional, but pretty sure that's just always a good thing

That Kneesovertoes guy on YouTube has some pretty great videos on knee rehabbing and strengthening.

A proper knee brace with a built in frame is needed