Holy hell, who cares what it was. Not saying that to anyone in particular, but everyone (media, Trump, the public).
A wacko shot at him, something related to the shot hit Trump. Whether it was a bullet or shrapnel doesn't change the fact he was lucky, and it doesn't make him more or less brave or cowardly. Without evidence to the contrary of the evidence we do have (bullet pic etc), there's no conspiracy either way.
If Trump wants to focus on this and on old guy Biden who isn't freaking running anymore, he can knock himself out while Harris chops him down like a fat old orange tree.