Zionism to me means that the Jews are entitled to self-determination, and that the modern state of Israel is the fulfillment of that promise.

Anti-Zionism is the negation of that idea; namely that Jews are not entitled to self-determination and therefore should live at the whims of the countries where they are a minority for their security.

Merely objecting to an Israeli policy or even a Jewish value is not intrinsically antisemitic. But if you criticize only Israel about some issue, and grant a free pass to everyone else on that same issue, that's when things become problematic.