It's a valid question and honestly very tough to answer.
I can only speak for my opinion, but I would say that criticisms of the Israeli government, the seeming disregard for civilians, the general tone set forth by certain politicians both here and abroad, etc... that's all fair game. Fuck Bibi. But when folks start dipping their toes into talking about "Zionism" is when things tend to get a little messy. I'm by no means saying that any criticism of Zionism is antisemitic, but I would say that most of the obviously antisemitic people have REALLY strong opinions on the topic.
And I'll acknowledge that there are bad actors claiming antisemitism in places where there is none. Fuck them, but please don't allow yourself to dismiss the notion of ANY antisemitism just because some jackasses are crying wolf.
And unrelated to the previous response, but another thing complicating the matter is that the groups, especially the unaffiliated third parties in America, are not speaking the same language. We've talked about it ad nauseum regarding the "From the River to the Sea" chant, but here's a paragraph that sums it up pretty well:
When your chant for peace is heard by many as a chant for destruction, how do we find a resolution?