Like you said, thyroid optimization is no different from TRT/HRT, cheap, effective, and with a solid, long standing safety record. If it's applicable to you, ie, free t4 is below the 80th percentile for your age, it'll have a greater impact on energy than anything else mentioned in this thread. You may even need to lower your Tirz dose to prevent excess weight loss.
Carderine for general fatigue is insane. It's useful for boosting endurance and cutting fat, but given a drug with those characteristics would've been a billion dollar blockbuster (especially in pre GLP times), and the pharma company developers chose to trash it, it's safe to assume the risk of causing cancer was clear to them.