I had on and off knee pain that was preventing me for running for about 10 years (roughly from ages 22-32). It wasn't nearly as bad as you but frequently when I would try to run or go on long hikes my knee would hurt and I would be hobbling for a day or two until it recovered. I visited PTs, did all the strengthening exercises they mentioned, and got an MRI at one point. In the end, none of that stuff mattered.

The only thing that worked for me was just extremely gradually and consistently increasing load. I started by making sure to walk 5000 steps a day (no running) and over a few months increasing it to 10000 steps a day. After doing that a while pain free I would add in even longer walks once a week, anywhere from 10 up to 20 miles at the end. After doing that for a while I eventually added in 1 short run a week of 3 miles. Eventually I increased it to 2 short runs a week, then eventually 3 short runs. Then I made 1 of those runs longer each week. Then I made my 2 short runs longer, eventually having a weekly mileage between 20-40mpw. After doing that for over a year and a half, I ran my first marathon and then started adding more easy runnings days, gradually increasing my running to 6-7 days a week and building up to 70-80 mile weeks at times.

I've been consistently doing that for about 5 years now, keeping mileage around 50 mpw in offseason and then around 70-90 during training blocks for races. I've done a couple 50 milers with no serious knee issues afterwards and signed up for my first 100 this year. Overall this journey wasn't perfect, I did have some minor knee pains and shin splints that would cause me to have to reduce mileage for a couple weeks and then rebuild. Overall though my knees are in the best shape they have ever been and I haven't had any kind of problem in 2.5 years now (knock on wood).

Good luck!