Zionism is the use of the right to self determination of the Jewish people in their ancestral homeland, currently as the state of Israel. If you deny the Jewish people the right to self determination, but support it for others, then that’s antisemitic of course.
You can criticize Israel’s current actions in the war in Gaza. Many Israelis do that all the time and have since early in the war. Most of those protesting in Israel against the Netanyahu government and for an end to the war wave Israeli flags and identify as Zionists themselves.
In practice, when people say they criticize Zionism, what they often actually want is for Israel to be destroyed. The state that is a home to and protects half of the Jews. The implications of that ends up pretty terribly for Jews. If you want half the world‘s Jews to be ethnically cleansed („go back to Poland“), of course that’s antisemitic.
It’s not like the Jews had a choice. They fled from persecution and Israel was the only place most of them could go to survive. It’s a state founded by refugees fleeing oppression, persecution, and genocide. That makes it fundamentally different from other settler countries like Australia, the USA, Canada, all Latin American countries, and many more.
Most Israeli Jews didn’t even come there themselves, they were born in the land and have no other home.
Yes, Palestinians also have a right to self determination. Two state solution is the best option for that. Sadly they refused several of the good offers they got, especially around the turn of the millennium.
Of course there are racist and hateful Israelis as well. The overall society has understandably hardened their stance towards Palestinians since October 7th.
You could say that about any ethnic nationalist movement.
Similar chants are common in the other direction as well.
A hundred years of conflict have taken their toll.