SHBG
SHBG — the molecular target that 2 compounds in the wiki act on.
In one line: A carrier protein that "handcuffs" testosterone — lowering it frees more up.
SHBG (sex-hormone-binding globulin) is a protein that grabs onto testosterone in your blood and holds it, making it unavailable to your muscles. Only the "free" testosterone that isn't handcuffed can actually do its job.
This is why some supplements (like boron and tongkat ali) can help even without raising total testosterone — they lower SHBG, so more of the testosterone you already have gets released to work. If most of your testosterone is handcuffed, freeing even a little makes a real difference.