Be cautious:
https://examine.com/nutrition/an-update-on-kombucha-understanding-risk-and-evaluating-toxicity/

As for magnesium, it depends on the diet. I do think it's hard to get too much dietary magnesium, but it's far easier to not get enough:

https://ods.od.nih.gov/factsheets/Magnesium-HealthProfessional/#h3

Keep in mind, we lose magnesium and electrolytes when we sweat. Low-carb intakes also cause low magnesium and electrolyte levels.

If you think your dietary intake is low, try 1 or 2 tabs of magnesium citrate, diglycinate, or tartate. Oxide is poorly absorbed; don't take that one.

Zinc and Vitamin D deficiencies are strongly correlated with lower testosterone in men. Magnesium less so, but given its importance in the metabolism of Vitamin D into its active form, I'd make it a priority.