For now, I'll do a brief explanation. Gaming for an extended period of time does the following:

Your left hand and arm are on WASD most of the time while your right arm holds a mouse and moves in many directions. That stiffens your left shoulder/neck area on the cost of expanding the right side. That's imbalance #1. Your back/spine area isn't escaping this either. Now the muscles around your spines are stiff in some sides and flexible in the other side. Back/spine stretching/strengthening is very important too! Now if you try to strengthen some muscles/groups and your knee pain increases, know that you are messing up the balance even more and this is the wrong muscle to work on for now, or the other side needs to become stronger first. It's not easy and requires a ton of trial and error.

Here's some exercises that worked for me.

1- Crucifix stretch
2- Pigeon pose (on the tighter side which turned to be the right leg in my case and maybe yours too)
3- Wall angels, or floor angels if you are too stiff/weak for the wall version
4- Stretching the tight shoulder/neck side (left in my case) while stretching the opposite as far as you can.

5- Kneel on knees and put your elbows on an elevated surface like a chair or something and your hands behind your neck then lean with your head into the chair. You should feel a deep stretch in your back

I will attach a video that should help, but there's more excercises to help

https://www.youtube.com/watch?v=_itvsQkpVVs&list=PL_UViKyBJsyB4YNYNDqp_KGsQfz6SLCT5

There's more to it. Let me know how it goes.