They might not be able to say anything. Advertising contract might have a clause saying they can’t speak of the details of their deal, or speak negatively about the sponsor.

Not to condone their actions, but what would Hamas care about getting supporters? Palestine situation hasn’t been helped much at all by international supporters, so it’s not like they care about that.

It’s not just that they don’t want their ads next nazi crap, it’s that they don’t want to put ads on a platform that has nazi crap. You make a platform friendly to nazis, you lose advertising.