ADL has been much more about pro-Israel than they have been about anti-antisemitism.
They know which way Israel's bread is buttered. Trump just removed all sanctions for the settlers, and allowed the sale of significantly bigger bombs to Israel on his first day.
Israel has a huge amount to gain from a Trump administration. ADL isn't going to blow that opportunity by calling out Elon's Nazi salute.
I don't see how Musk's two Nazi salutes can be defended when he deliberately did it twice and has a history of supporting extreme right-wing views.