Criticism of Israel CAN be anti-Semitic, but it isn't always.
For example - If a prominent Jewish entertainer has done something - let's say David Baddiel has released a new children's book, and is holding an online Q&A about it, but instead of asking about the book, some people repeatedly ask him to denounce the actions of the Israeli state, and message him criticising the state of Israel - something he has absolutely nothing to do with.
that would seem pretty anti-Semitic, and it is the kind of thing that happens a lot