The honest rule for supplements runs through this whole part: they help if you're genuinely deficient, and mostly don't if you're not. A few micronutrients matter for testosterone — by correcting a shortfall, not by lifting a healthy man's level.
Low vitamin D is associated with lower testosterone, and correcting a genuine deficiency may modestly help. But supplementing men who are already replete does not reliably raise testosterone — the trials are mixed and the effect small. Worth fixing for bone, immune and general health regardless; not a reliable testosterone lever on its own. Evidence ●●●○○
Zinc is needed to make testosterone, and deficiency lowers it — so correcting a shortfall helps, but there's no benefit from extra zinc if you're already replete. Heavy sweaters and endurance athletes are more prone to running low. Evidence ●●●○○ (deficiency only)
Magnesium may nudge free testosterone slightly by affecting how much binds to SHBG; boron can lower SHBG and raise free T in small studies. Both are modest and preliminary — reasonable to keep intake adequate, not something to expect a real change from. Evidence ●●○○○
Fix shortfalls, don't megadose
If you're low in vitamin D or zinc, correcting it is worthwhile and may help testosterone a little. Loading a man who's already replete does nothing for his level and, for zinc especially, high chronic doses cause their own problems (copper deficiency). More is not better.
The Testosterone Guide