i killed my RSI that I had for YEARS by seriously over-hauling my workspace. I also went to occupational therapists who helped me figure out what I was doing wrong and how to fix it.

I use a moonlander split keyboard so my shoulders are properly spread out instead of hunched together, and my wrists and arms can fall at a more reasonable angle.

I use a "tall" ergo mouse. This was a huge upgrade from my small mouse and I definitely noticed the improvement.

I figured out how to properly set the height of my desk such that I was not craning my arms up or down.

i fixed my "cross-legged" posture I used to use while sitting at the computer.

And finally: I built up a weight lifting habit that strengthened my entire body.

Of all of them, weight lifting likely had the biggest impact.