If ENDURANCE workouts tire you out and you find human growth hormone (HGH) helpful for recovery, it might be beneficial. But from my experience, taking HGH at 3 IUs a day led to water weight gain and some joint tightness, which didn't support my endurance goals. What I've found most effective is maintaining a generous testosterone replacement therapy (TRT) range of 175-250, adding carnitine if it suits you, and eating in a way that aligns with your body composition for your specific endurance goals—like for swimming, cycling, climbing, or grappling, each might require slightly different body compositions to maximize endurance.
Taurine can assist with pumps and cramps, and it's important to ensure your electrolyte levels are well-maintained. I'd suggest holding off on cardarine until you've established a solid cardio progression plan and have made some progress. Using it only when you hit a plateau and then discontinuing it later on might still allow progress without relying on it all the time.