I think you are trying too hard. 20 minutes on a stair climber is intense.

"My mentallity is to push through the fatigue in order to reach my goal of recovering."

You are not rebuilding injured muscles. If you sense the very beginning of fatigue, take a break, even if it is only momentary as in a "stop and think" break.

Your brain has its own schedule of recovery. You can not force it. You should add D3 and B-12 to your regimen and maybe some magnesium. Nutrition is a long term aid to your brain's effort to recover.

You should try to learn how to recognize mental fatigue and separate it from physical fatigue. Those first moments of mental fatigue need to be recognized so you can take those short breaks.

It is more of a learning process that push through effort.

My best to you.