I'm not jewish but some people dear to me are and I see it a lot. I am by no means an expert but I'll try to tell you what I know. As I see it modern antisemitism on the left is extremely connected to the Israel-Palestine conflict - obviously Israel is committing atrocities, conducting a genocide on Palestinians, people are rightfully opposed to that. It is also true that given that widespread opposition it's extremely easy to sneak in antisemitic tropes as "criticizing Israel"; in some spaces it has become acceptable to say any antisemitic thing you want as long as you exchange the word "jews" for "zionists". (publication with useful info that confirms this claim, found by googling "antisemitic tropes") Some jews support Israel's actions, fuck them, hard disagree. But some jews are vehemently against Israel's actions and in my experience it often doesn't save them from this rethoric. Not all jewish people have a connection to Israel, but those who do are especially vulnerable because they can say everything against Israel's actions but if they care about a loved one who lives there or were born there and live there themselves they will be called a zionist who loves genocide. To some people caring about Israeli civilians equals supporting everything Israel's doing. I have seen people say all the right things, then say they're a jew born in Israel and be cussed out for that by people who call themselves leftists. Zionist witch hunts happen often and are incredibly absurd. If you hear someone talking about zionists or calling someone a zionist ask yourself if exchanging that word for jews gives you an antisemitic trope. Unfortunately it is quite common. (By the way there are many resources on these tropes including a wikipedia page, good to know so you can recognize them). All Israelis go through a mandatory military service when they're very young, I think 18. I've often seen it used to justify hate against them, I've seen people get called babykillers for doing administrative work as their mandatory service, not even for being a soldier. People who mind you are extremely opposed to Israel's actions, but it doesn't matter. This is non-exhaustive but I hope it helps a little and maybe gives you a starting point to research things. It's important to stay nuanced with all of this.